Dai Cuong Huu Co

7/25/2019 Dai Cuong Huu Co

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CHNG 1: I CNG VHO HU C1.1. i tng ca ho hc hu c

- Ho hc hu c l mn khoa hc nghin cu thnh phn v tnh cht cc hpcht ca cacbon.- Trong thnh phn ca cc hp cht hu c, ngoi cacbon cn cha nhiu nguyntkhc nh: H, O, N, S, P, halogen Nhng cacbon c coi l nguyn tcbncu to nn cc hp cht hu c.- Ho hc hu cnhanh chng trthnh mt ngnh khoa hc ring v cc nguynnhn di y:+ Slng cc hp cht hu ctng ln nhanh chng v t ti con skhng lkhong 5 triu cht, trong c nhng cht ng vai tr v cng quan trng ivi s sng nhprotein, axit nucleoic, hocmon v ni chung, n lm cho hohu cng vai tr to ln v ng dng phong ph trong kinh t, quc phng vi sng.+ Nguyn nhn dn n stn ti mt slng rt ln cc hp cht hu cl ch cc nguyn t cacbon c kh nng c bit l va c th lin kt vi ccnguyn t ca cc nguyn t khc v va c th lin kt vi nhau thnh mchcacbon cc kiu khc nhau. Do , cc hp cht hu cxut hin cc hin tngng ng, ng phn, hbin v nhng biu hin phong ph vho lp th.+ Cc lin kt chyu trong ho hu cl lin kt cng ho tr, nn c tnh cht lhc v ho hc khc cc hp chy v c. Cc hp cht hu cmn cm vi nhithn, khng bn nhit cao, a s chy c, t tan trong nc, s tan cthng t hoc khng phn li thnh ion. Cc phn ng thng chm, thun nghchv theo nhiu hng.1.2. Slc lch spht trin ca ho hc hu c- T thi xa xa, ngi ta bit iu chv sdng mt scht hu ctrongi sng nhgim, mt scht mu hu c, ru etylic, Thi kgikim thut,cc nh ho hc bit iu chmt scht hu cnhete etylic, ur- Vo cui thkXVIII, u thkXIX, cc nh ho hc chit tch c tng, thc vt nhiu axit hu cnhaxit oxalic, axit xitric, axit lactic v mt sbazhu c. Nm 1806, ln u tin Berzelius dng danh tho hc hu c

ch ngnh ho hc nghin cu cc hp cht c ngun gc ng, thc vt. Thiim ny c thxem nhim mc nh du sra i ca mn ho hc hu c.- Nm 1815, Berzelius a ra thuyt lc sng, mt lun thuyt duy tm, chorng cc hp cht hu c ch c th to ra trong c thng, thc vt nhmtlc sng c bit m bn tay con ngi khng thiu chc chng trongcc bnh, l, ng nghim nhi vi cc cht v c.- Thuyt lc sng thng trho hc hu ctrong nhiu nm. Sau thuytny dn dn bnh nhcc cng trnh tng hp cc cht hu ctcc cht vc.


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- Nm 1824, Wohler tng hp c axit oxalic, mt axit hu c in hnh(bng cch thuphn dixian l mt cht v c). Nm 1828, cng chnh Wohler

tng hp c ure (vn c trong nc tiu ng vt) tamoni xyanat, cng l mtcht v c:NH4CNO H2N CO NH2

Chnh pht minh ny lm sp bc tng ngn cch trc gia hohc v cv ho hc hu c, lm cho cc nh ha hc tin rng c thttng hpc cc cht hu ctrong phng th nghim m khng cn c s tham gia camt lc sng no c.- Tip theo , Bectl tng hp c cht bo (1854) v Bulerp tng hpc ng glucoza tformalin (1861).- Cho n nay, hng triu cht hu c c tng hp trong cc phng th

nghim v trong cng nghip. Khng nhng con ngi bt chc c thinnhin trong nhiu lnh vc m con ngi cn sng to ra c nhiu vt liu huc, nhiu cht hu ccc kquan trng, qu gi khng c trong tnhin.- Tuy nhin, tn gi hp cht hu c vn c duy tr, nhng khng phi vingha nhtrc y l cc cht c ngun gc ng, thc vt m n mang mtni dung mi, l cc hp cht ca cacbon.1.3. Nhng quan im vcu to ca hp cht hu c

Cu to ca hp cht hu c l s phn b ca cc nguyn t hoc nhmnguyn ttrong khng gian ca mt phn t.1.3.1. Thuyt gc (Radial, k hiu R)

Thuyt cu to ho hc ca cc hp cht hu cc pht trin mnh u thkXIX. Tnhng cng trnh ho hc ca Lavoisier, Berzelius, Wohler,Liebig cho thy trong nhng phn ng hu c c nhng phn cht c cu trckhng thay i chuyn tcht u sang cht cui gi l gc. Quan nim ny cho ra i thuyt cu to ho hc u tin l thuyt gc. Thuyt gc cho rng,phn thu cgm 2 phn:- Gc l phn khng bin i trong cc qu trnh chuyn ha ha hc.

V d: Gc axetyl: CH3CO-Gc benzoyl: C6H5CO-

- Phn kt hp vi gc l cc nguyn thay nhm nguyn tkhc nhau.*u im: Phn loi c mt scc hp cht ha hc hu ctheo gc cuto. T c thdon c tnh cht ca cc nhm hu c.

*Nhc im: Ch phn bit c nhng hp cht n gin, khng c ngha i vi cc hp cht phc tp. Do phm vi ng dng b.1.3.2.Thuyt kiu

Thuyt kiu ca Dumas ra i chia ra lm hai dng:- Dng ho hc gm nhng cht c tnh cht ho hc ging nhau nhaxit axeticv axit cloaxetic.


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- Dng chc gm nhng cht c cng snguyn tnhnhau nhng tnh chtkhc nhau nhaxit axetic v ru etylic.

Theo thuyt kiu ny, ngi ta thit lp c nhiu kiu hp cht hu cnh:- Kiu nc ca Williamson:

- Kiu amin ca Wurtz v Hofmanm:

H

H

H

N

- Kiu clorua hiro ca Gerhardt:H

Cl

CH3

Cl

C2H5

Cl

C2H3O

Clhyrcloruam tylclorua tylclorua ax tylcloru

Trong quan trng nht l kiu metan ca Kkul:H

H

H

H

C

Ngi ta xc nh c rng, cc hp cht hu cc c trng bng

nhng phn ng kiu xc nh.* u im:

+ Thuyt kiu c ng gp to ln vo vic phn loi cc hpcht hu c, thun li cho vic tm kim.

+ Nghin cu nhng phn khng thay i trong cc chuyn ho hohc v cng gii thch c phn no sthay i .

* Nhc im:

+ Do skiu nhiu nn rt phc tp trong vn phn loi, hn chtrong vic sdng.+ C nhng hp cht hu ckhng th sp xp theo mt kiu no

c.1.3.3. Thuyt Butlerop (ng tca ho hc hu c)

Ni dung ca thuyt cu to ho hc ca Butlerop bao gm cc lun im:- Tt ccc nguyn ttrong hp cht hu ckt hp vi nhau theo mt trt

txc nh. Trong vic kt hp , cc nguyn t tiu ph mt phn i lc hohc ca mnh. Trt tkt hp ca cc nguyn tv c tnh ca cc lin kt trongphn tl cu to ho hc.

H

HO

CH3

HO

CH3O

CH3


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- Nguyn tca cc nguyn tto nn phn tlin kt vi nhau theo ngho tr ca mnh. Trong phn t cht hu c, cacbon bao gi cng c ho tr4.

Cc nguyn t cacbon chng nhng c th lin kt vi cc nguyn t ca ccnguyn tkhc m cn c thlin kt vi nhau thnh mch.- Tnh cht ca cc cht khng chph thuc vo thnh phn v s lng

nguyn tca cc nguyn tm cn phthuc vo cu to ho hc ca hp cht.- Cu to ho hc ca cc cht c thxc nh c khi nghin cu tnh

cht ca chng. Cu to ho hc ca mi cht c thbiu din bng mt cng thcxc nh l cng thc cu to. Cng thc cu to va phn nh cu to ho hcca phn tva thhin nhng tnh cht cbn ca hp cht.

- Tnh cht ho hc ca mi nguyn tv nhm nguyn t trong phn tkhng phi l bt bin m thay i tuthuc vo cc nguyn tv nhm nguyn

tlin kt trc tip vi nhau mnh hn nh hng gin tip.Ththch qua thi gian, thuyt cu to ho hc tra ng n v su sc.Tnhng lun im sgin y, ngy nay pht trin thnh nhng thuyt hini vcu to v lin kt, vhiu ng, vho hc lp th,1.4. Cch biu din cng thc cu to hp cht hu c

Cng thc cu to phng biu din cu trc ca phn tquy c trn mtmt phng, thng l mt phng giy.1.4.1. Cng thc Lewis

Cng thc Lewis biu din cc lin kt gia cc phn t hay s electronho trca mi nguyn tbng selectron. Selectron l bng tng electron ca

cc nguyn tng gp vo v cc nguyn tc xu hng to trng thi electronln nht c thc c vng electron bn vng ca kh tr.V d:

O C O

C

H

H

H

H

C C

H

H

H

H Cc cng thc c thmang in tch, thng gi l in tch hnh thc hay

quy c:

N+H

H

H

H

Ion amoni

C

H

O

H

H

Ion metoxit Khi nhng tiu phn khng c vng bt t th thng l nhng tiu

phn trung gian khng bn, c khnng phn ng cao v trong phn ng c xuhng nhanh to thnh cu trc electron bt t:


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H

HH C+

Cation metyl

H

HH C

* u im:Dk hiu, cho thy c bn cht ca qu trnh phn tch.*Nhc im:Phc tp cho qu trnh biu din, dgy sai st. Trong mt

strng hp khng biu din c.1.4.2. Cng thc Kekul

n gin trong cch biu din ca Lewis, ngi ta quy c biu dincc lin kt trong phn tbng vch ngang thay cho cp electron lin kt.V d:

N HH

H

H

C

H

H O

H

C HH

H

C HH

H

Trong cc hp cht c mang in tch cng c th thay thkin kt bng

mi tn tcht cho ti cht nhn:

H O N

O

O H O N

O

OHay

n gin trong cch biu din cng thc, c thn cc gch lin kt, n

mt phn hay ton phn tuthuc vo yu cu cch biu din, ng thi cng bqua cc cp electron khng lin kt, gi l cng thc rt gn:

CH3CH2CH3, CH3 CH2 CH3, CH3CH2CH2 HNgoi ra, mt cht c thbiu din di nhiu dng cng thc, chng hn:

CH3 CH2 CH3 CH3 CH2

CH3

CH2

CH3

CH3

* u im:Khc phc nhc im ca cng thc Lewis, n gin v phnnh tht bn cht ca lin kt.*Nhc im:Khng thy sgp chung electron. Trong trng hp phn

ct dly th khng thy c hin tng.Ch : Trong mt strng hp c bit cc hp cht hu cmch vng,

ngi ta thng khng biu din k hiu ca cc nguyn tcacbon v hidro.1.5. Danh php hp cht hu c

C 4 loi danh php chyu:1.5.1. Danh php thng thng

Gc metyl


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L tn c gi theo ngun gc thu nhn c cht , theo tn ca ngitm ra n hay mun ca ngi tm ra n, theo phng php thu nhn c cht

.V d: Axit fomic: HCOOH (Fomica: Kin)Axit axetic: CH3COOH (Acetus: Gim)Mentol: C10H20O (Mentha piperita: Bc h)

1.5.2. Danh php hp l (Thun chng)Ly tn ca mt hp cht hu clm tn gi u sau gi tn ca cc hp

cht hu ckhc tng ttheo tn ca cc cht hu cu.

V d:

C OH

H

H

H

Cacbinol

C OH

H

H

CH3

Metyl Cacbinol

C OH

H

C6H5

CH3

Metyl Phenyl Cacbinol Nhc im: i vi cc hp cht phc tp th khng thgi tn c.

1.5.3. Danh php thng miL tn ca cc hp cht ho hc hu cc sdng trn thtrng do cc

hng sn xut t tn.V d: Cc loi thuc nhm: Rongalit C (NaHSO2.CH2O.2H2O): dng in hoa

Rongal P ( Dn xut ca axit sunfonic): dng nhum huyn ph.1.5.4. Danh php IUPAC (Hip hi ho hc quc t: International Union Pine

And Applycation Chemistry)1.5.4.1. Tn gc - chc

V d:CH3CH2 Cl CH3CH2 O COCH3 CH3CH2 O CH3

Etyl clorua Etyl axetat Etyl metyl ete1.5.4.2. Tn thay thTn khng y :

V d:H3C CH3 H3C CH2Cl H2C = CH2

Etan Cloetan Etan

TN PHN GC TN PHN NH CHC

TN PHN TH TN MCH CACBON CHNH TN PHN NH CHC(c thkhng c) (bt buc phi c) (bt buc phi c)


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* Tn nhm th:Cc nguyn tca cc nguyn tth gi tn theo tng nguyn t

OH : HirxylOR : AncoxylCH3O : Mtoxyl

C6H5O : PhenolxylCH3CO : AxetylC6H5 : PhenylC6H5CH2 : Benzyl

NO2 : Nitro

NH2 : Amino

CN : Nitryl

SH : Mcaptan

SO3H : SunfonicR - : Ankyl

* Chn mch chnh: Chn mch cacbon di nht cha cc nguyn tcacbon lin kt cacbon lm mch chnh. Chn mt nhm chc c u tin nhtlm nhm chc chnh, cc chc cn li l phn th.

u tin nhm chc chnh: -COOH > -COO- > -CHO > -CO- >-OH >-

NH2> -O-* nh stht:Ta nh sthttbn phi sang bn tri hoc tri qua sao cho tng cc

chsca cc nhm thl nhnht. Trng hp khi nh stu ny n ukia m thu c mt sdy chsca cc nhm mch nhnh khc nhau th phisp xp chng li theo thttng dn. Dy c tng cc chsnhnht c xeml dy c chsu nhnht.

V d:

* Tn phn nh chc:An, en, in, ol, al, on, oicTn y : Cu hnh + du quang hot + tn gi khng y gi tn hp cht hu c, cn thuc tn cc sm v tn mch cacbon nhsau:

CH3 CH2 CH CH2 CH3

CH33-Metyl pentan

CH3 CH CH CH2 CH3

CH32-Metyl pentan

2


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SM MCH CACBON CHNH

1: mono C met

2: i C C et3: tri C C C prop

4: tetra C C C C but

5: penta C C C C C pent

6: hexa C C C C C C hex

7: hepta C C C C C C C hep

8: octa C C C C C C C C oct

9: nona C C C C C C C C C non

10: deca C C C C C C C C C C dek

1.6. Phn loi cc hp cht hu cHp cht hu cc phn thnh hidrocacbon v dn xut ca hidrocacbon.Hidrocacbon l nhng hp cht c to thnh thai nguyn tC v H. Gm 3loi:Hidrocabon no (Ankan): CH4, C2H6Hidrocacbon khng no gm anken: C2H4v ankin: C2H2Hidrocacbon thm (Aren): C6H6Dn xut ca hidrocacbon l nhng hp cht m trong phn tngoi C, H racn c mt hay nhiu nguyn t ca cc nguyn t khc nh O, N, S,halogenbao gm: dn xut halogen nhCH3Cl, ancol nh: CH3OH, axit nh:CH3COOH,


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CHNG 2: CU TRC KHNG GIAN PHN THPCHT HU C

2.1. Chit tch v tinh chhp cht hu cCc hp cht hu c khi mi iu chc hoc tch tng thc vt,

thng dng hn hp khng tinh khit. V vy mun nghin cu chng, munphn tch nh tnh hay nh lng chng th nhim v trc tin l phi tchchng thnh tng cht ring bit, dng tng i nguyn cht.2.1.1. Tinh chcht rn2.1.1.1. Phng php kt tinha. Khi nim

Kt tinh l mt qu trnh bin i pha ca mt cht trn sang lng khi ho

tan cht rn trong mt dung dch bo ho, sau lm lnh dung dch bo ho thu c cht rn kt tinhCh : Cht rn kt tinh khc kt ta:+ Cht rn kt tinh: C ssp xp li cc phn tv c cu trc mng tinh

th.+ Kt ta: Kt ta tinh thv kt ta v nh hnh.

b. Csl thuytPhng php kt tinh c dng tch v tinh chcc cht hu c rn,

da trn nguyn tc l cc cht khc nhau c ho tan khc nhau trong cng mtdung mi.

Dung mi thch hp c la chn thng l dung mi trong ho tanca cht cn tinh ch tng kh nhanh theo nhit , tan km nhit thng.Dung mi khng tan trong tp cht, dung mi khng c lc tng tc vmt hohc i vi cht kt tinh. Dung mi sau khi kt tinh li phi dbay hi. Dung mila chn phi dkim, rtin.

Bng cch to dung dch bo ho nhit cao (thng l nhit si cadung mi), sau ngui dung dch thu c, cht cn tinh chslng xungy bnh (hay y cc), cc tp cht sli trong dung dch. Bng cch kt tinhli mt s ln trong cng mt dung mi, hoc trong cc dung mi khc nhau,ngi ta c ththu c tinh thcht cn tinh chdng kh tinh khit.

Cng c khi ngi ta dng mt dung mi c ho tan vi tp cht nhiuhn loi tp cht khi cht rn cn tinh ch.

Dung mi thng dng l nc, alcol etylic, ancol metylic hay mt alcolthch hp khc, axeton, axit axetic, ete, benzen, cloroform, etyl axetat....hoc ikhi hn hp gia chng.

Khi cn tch hai hay nhiu cht c cha trong hn hp vi nhng lngtng ng nhau, ngi ta dng phng php kt tinh phn on.

Cht kt tinh li c ht u v trng.


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Khi c cht rn kt tinh, ta cn xc nh nhit nng chy ca n bngng mao qun gn vi nhit knhng trong mt dung mi c nhisi cao, hoc

cch khng kh, hoc nhmt my chuyn dng ri i chiu vi hng svt lca cht cho, bit c cht tinh khit hon ton cha.2.1.1.2. Phng php thng hoaa. Khi nim

Thng hoa l mt qu trnh bin i pha ca mt cht ttrng thi rn sangtrng thi hi m khng thng qua trng thi lng.b. Csl thuyt

Mt scht nhit, long no, naphtalen, menton, clorua st (II),... c khnng thng hoa, v vy ngi ta c th dng phng php thng hoa p sutthng hoc p sut thp tinh chchng.

Phng php tin hnh: Gia nhit mt cht rn bay hi, lm lnh hi cacht rn th ta sthu c cht rn kt tinh c tinh khit cao, cn tp chtkhng thng hoa th nm li y bnh.

* u im: Cng ngh n gin, thi gian ngn, tinh khit cao, githnh r.

* Nhc im:Trong thc tkhng c nhiu cht thng hoa.2.1.2. Tinh chcht lng2.1.2.1. Phng php chng cta. Khi nim

Chng ct l qu trnh lm bay hi cht lng, sau l lnh v thu chtlng c tinh khit cao hn.b. Cc phng php chng ct- Chng ct n gin

Trong trng hp cn tinh chmt cht lng, tch n ra khi tp cht rnkhng bay hi, ta chcn tin hnh chng ct n gin, ngha l chuyn n sangpha hi trong mt bnh ct c nhnh ri ngng thi ca n bng ng sinh hnvo mt bnh hng khc.- Chng ct phn on

Phng php chng ct phn on dng tch hai hay nhiu cht lng c

nhit si khc nhau tan ln hon ton trong nhau da trn nguyn tc c sphn bkhc nhau vthnh phn cc cu tgia pha lng v pha hi trng thicn bng (cng nhit )

Nu hai cht lng khng tng tc vi nhau, c thbiu din sphthucca nhit si ca cht lng v nhit ngng tca hi phthuc vo thnhphn hn hp hai cht (hnh 2.1)


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Hnh 2.1

Qua hnh 2.1 nhn thy rng, bng cch lp i lp li nhiu ln qu trnhbay hi - ngng t, bay hi - ngng tli,... ta dn dn c ththu c cu tAc nhit si thp hn dng gn nhtinh khit. V vy, ngi ta dng phngphp tinh luyn bng cch lp trn bnh ngng mt ct cao c nhiu a gip chovic ti to qu trnh bay hi - ngng ttrn. Nhvy, cht lng A dbay hi dndn thot ln trn trng thi ngy cng tinh khit, cn cht lng B c nhit sicao hn, ngng ttrli bnh ct. C thdng loi ct lp y cc ng thutinhhay s thay cho ct ni trn v hiu qu ca ct c tnh bng sa lthuyt.

Trong trng hp c tng tc yu gia hai cht lng (solvat ho hay t

hp) th thu c hai dng thbiu din sphthuc nhit si v ngng tvo thnh phn hn hp: mt dng vi nhit si ca hn hp ng ph cctiu(hnh 2.2a) v mt dng vi nhit si cc i (hnh 2.2b).

T0

TA

A BX2 X1 X1

T1

T2

T0

Thnh phn

A B A BThnh phn Thnh phnX0 X0

tA

tBt

tA

tB

C

Ct

Hnh 2.2a Hnh 2.2b


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Trong trng hp hn hp ng ph c nhit si cc tiu (thp hn haicu tban u), cng ln pha trn ca ct ct, hn hp hi v lng cng gn thnh

phn ca hn hp ng ph, trong bnh ct scn li cht A hay B nguyn cht tutheo ta xut pht thn hp c thnh phn pha bn tri hay bn phi hnh 2.2a.Trong hn hp ng ph c nhit si cc i, cng ln pha trn ca ct ct thcng giu cu tA hoc B, cn li trong bnh s l hn hp cng gn vi thangphn ca hn hp ng ph (hnh 2.2b).- Chng ct chn khng (hay gim p)

Khi cn chng ct mt cht lng dbphn hunhit cao, ngi taphi dng phng php ct chn khng, tc l dng bm ht gim p sut trnbmt cht lng. V cht lng ssi khi p sut hi ring phn t n p sut khquyn, nn bng phng php ny, ngi ta c thgim c nhit si ca nmt cch ng k, trnh hin tng phn hu hay chy n. Nh phng trnhClapayron - clausius, ngi ta c thtnh c sphthuc ca p sut hi mtcht vo nhit . Tuy nhin, c thp dng qui lut thc nghim gn ng nhsau: Khi p sut kh quyn trn bmt mt cht lng gim i mt na, nhit sica n bhthp i khong 150C.- Ct li cun hi nc

Ta cng c th tinh ch mt cht lng khng ho tan trong nc, bngphng php ct li cun theo hi nc him si ca n.

Phng php ny da trn nguyn tc: Khi hai hay nhiu cht lng khngtrn ln vi nhau nm trong mt hn hp, p sut chung p ca chng bng tng psut ring phn p1+p2, ngha l n lun lun ln hn p sut hi ring phn ca

tng cu t bt k no. Do , nhit si ca hn hp s thp hn nhit hnnhit si ca cu tsi thp nht. Tlhi ct sang bnh ngng (vsmol) sbng tlp sut hi ring phn ca chng nhit si ca hn hp. Nhvy tac thtnh ton c lng nc cn thit li cun ht cht cn tinh ch.

Sau khi dng phng php ct li cun theo hi nc, thng ta phichit tch cc cht cn tinh chra khi nc bng mt dung mi thch hp, ri litin hnh ct phn on tch dung mi. Cui cng chng ly cht tinh khitbng bnh ct c gn nhit kdi p sut thng hay gim p, vi skim tranhit ca cht cn tinh ch.- Phng php chit

Chit l dng mt dung mi thch hp c khnng ho tan cht ang cntch v tinh ch tch cht ra khi mi trng rn hoc lng khc. Thngngi ta dng mt dung mi si thp v t tan trong nc nhete, cloroform chit tch cht hu c t mi trng nc (cc cht hu c cn tinh ch nythng tan t trong nc hoc dng nhtng ln vi nc). Sau khi lc dungmi vi hn hp cht cn tinh chv nc, cht schuyn phn ln ln dungmi v ta c thdng phu chit tch ring dung dch thu c khi nc.

Bng cch lp li vic chit mt sln, ta c thtch c hon ton chtcn tinh chvo dung mi chn, sau ct loi dung mi v ct ly cht tinhkhit nhit v p sut thch hp.


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13

Ngi ta cng thng chit mt cht t hn hp rn bng mt dung mihoc hn hp dung mi vi mt dng cchuyn dng c bit gi l bnh cha

Soxhlet. Dung mi c un nng, cho bay hi lin tc chy vo bnh cha hnhp cn chit tch (thng c gi bng giy lc), n sho tan cht rn cn tinhchv nhmt ng xiphng, dung dch chy xung bnh cu bn di, dung minguyn cht li tip tc c ct ln. Qu trnh c tip tc cho n khi schittch c hon ton.

Phng php ny tit kim c dung mi v t hiu qutng i cao.2.1.3. Phng php sc k2.1.3.1. Khi nim

Phng php sc k c Xvt pht minh ra tch cc cht bng hp phtu thkny (1903), n nay tr thnh mt phng php tinh ch, nhtnh, nh lng rt quan trng trong ho hc hu c, c pht trin rt mnh vc sdng rng ri trong hu ht cc phng th nghim hin i.

Nguyn tc chung ca phng php sc k nhsau: hn hp cht nghincu pha lng (dung dch) hay pha kh c cho i qua bmt cht hp phpha rn hay pha lng kh bay hi. Do khnng tng tc vi pha tnh khc nhaunn cc cht khc nhau trong hn hp nghin cu chuyn ng vi vn tc khcnhauv dn c phn tch ra tng cu tring bit. Ngi ta phn chia ra thnhcc loi sc k khc nhau.2.1.3.2. Sc k ct (sc k hp ph)

Trong phng php sc k ct, ngi ta dng cc ct thutinh hay i khibng kim loi, c kch thc thng thng l 15x1; 25x2; 40x3 hoc 60x4 cm;

dng cc cht hp phdng bt , thng l nhm oxyt, silicagel, tinh bt, barisunfat... hoc mt cht bt kkhc khng tng tc vi cht nghin cu v dungmi. Hn hp cht nghin cu c ho tan trong mt dung mi trthch hp vcho chy qua ct. Cc cht trong hn hp nghin cu dn dn tch khi nhau vchng chim cc vtr khc nhau trn ct hp ph. V lc u ngi ta tin hnhtrn ct th nghim vi cc cht mu, khi chng ta tch ra to thnh cc khoanhmu khc nhau trn ng hp phnn phng php ny c gi l phng phpsc k. Sau ngi ta tch ring tng cht hoc bng cch ct ct hp phthnhtng on ng vi tng cht, hoc lin tc thm dung mi, cc cht sln ltc ra tri v thot ra bnh hng cc thi im khc nhau.

C thdng phng php ny tch cc cht khng c mu, nhng phidng cc cht chthhay thuc ththch hp nhn bit khi no chng bt uthot ra bnh hng.2.1.3.3. Sc k giy

Sc k giy l mt dng c bit ca sc k phn bdo Consden, Gordonv Martin pht minh nm 1944. Pha tnh y l nc thm trn giy lc c bit(xenlulza tinh khit). Dung dch cht nghin cu c chm trn mt u ca digiy (cch mp giy chng 2,5cm) v mi git cch nhau chng 2cm. Ngi tathng nhng thi cdung dch mu bit so snh. Sau u giy lc


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14

c nhng trong mt dung mi hay hn hp dung mi thch hp bo honc.

Do lc mao dn, dung mi s thm dn ln giy sc k, ko theo chtnghin cu chuyn ng ln pha trn v to vt trn giy m ngi ta c thnhnbit c bng mt thng hoc bng cht chth. TsRtgia dch chuynca cht nghin cu v dung mi c gi l hng ssc k, hng sny l ilng quan trng c trung cho tng cht.

thu c kt qutch tt hn, ngi ta c thlp li thao tc trn vimt dung mi khc v theo chiu thng gc vi chiu chy ln trc (sc k phnbhai chiu).

Sc k giy thng dng nh tch cc cht, nhng cng c thdng nh lng sbda vo m v tit din ca vt cht nghin cu.2.1.3.4. Sc k lp mng

Phng php ny c Izmailop v Schreiber ngh tnm 1938, cStan pht trin v hon thin (1955), khin n c ng dng rt rng ri.

Ngi ta trng mt lp mng cht hp ph(Al2O3, silicagen) ln mt tmknh kch thc khong 10x12 cm hoc 20x20 cm, chm mt git cht nghin culn mt u bn (cch mp khong 2cm) ri cho dung mi chy nhsc k giy.

Phng php sc k lp mng thng cho hiu qu tch cao, thi gianngn, lng cht t, thng c dng nh tnh v tch cc hp cht thinnhin. N cng c cc nh ho hc tng hp sdng thng xuyn nhanhchng phn tch cc cht thu c trong phn ng.2.1.3.5. Sc k kh lng

Nhng nm gn y sc k kh lng (sc k kh) c pht trin mnh m,mra khnng ln trong phn tch v tch cc hp cht dbay hi. Phng phpthng thng l cho vi microlit cht lng phn tch vo thit bbay hi ri dngdng kh mang (thng l He) li cun hi ca chng qua mt ng di nung nngnp y mt cht rn xp (gch chu la tn nh, nhm oxyt, silicagel, than hottnh...) c tm bng cht lng kh bay hi nhdu silicon, polyetylen glycol,cc este si cao...Khi xy ra sphn bcc cht gia pha lng v pha kh, ngthi chcn c skhc nhau nhtrong sphn bny gia cc cu ttrong hnhp cng phn tch hon ton cc cht lng trong hn hp, v n c lp ilp li nhiu ln trong ng di. Ngi ta thng nhn bit tng cht thot ra cui

ng bng cch o s thay i dn nhit ca kh thot ra. Tuy nhin vic phthin mt pic trong ssc k kh mi l iu kin cn, nhng cha vtinhkhit ca mt cht, phng php sc k kh vn rt hu ch khi phn tch mtlng nhhn hp cng nhtch v tinh chcc cht.

Cn nhn mnh rng, trong phng php sc k, ni chung cu trc phn tca cc hp cht c nh hng ln n cn bng hp ph, cng nhhsphn bca chng gia cc pha, do lin quan cht chn hng sRt. V vy kt quphn tch sc k cng cho ta thy nhng thng tin bch vcu trc ca hp cht.


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Sau qu trnh tinh ch, ta cn kim tra tinh khit ca hp cht thu cbng cch o nhit nng chy (i vi cht rn) hoc nhit si (i vi cht

lng) hoc o tkhi, chskhc x, chp ph...Mt cht c coi l tinh khit nu qua nhiu ln tinh ch, cc hng svtl ca n khng thay i.2.2. Cng thc phn thp cht hu c

xc nh c cng thc phn tcc cht hu c, ngi ta tin hnhxc nh cc thnh phn nguyn tv khi lng phn tca chng.

2.2.1. Phn tch nguyn tCc cht hu cngoi cacbon cn thng c hydro, oxy, nit, halogen, lu

hunh,... xc nh sc mt v hm lng ca chng, ngi ta sdng ccphng php nh tnh v nh lng ring.2.2.1.1. Xc nh cacbon v hydro

Sc mt ca cacbon v hydro trong mt hp cht thng c xc nhbng cch t chy hp cht trong oxi, vi xc tc l CuO:

CxHyOz + (x + y/4 - z/2) O2 x CO2 + y/2 H2OCO2thot ra c nhn bit bng phn ng lm c nc vi trong:

Ca(OH)2 + CO2 CaCO3 + H2OH2O c nhn bit bng cch ngng t trn phn lnh ca ng t hay bngCuSO4khan.

nh lng cacbon v hydro, ngi ta t chy mt lng cn chnh xccht nghin cu bng dng oxy c mt CuO trong ng thch anh, ri hp thhinc thot ra bng perclorat magie (MgClO4); CO2hp thbng tm st (NaOH).

Cc cht hp thny ng trong ng chU v khi lng ca chng c cnchnh xc trc v sau khi th nghim kt thc. Hiu skhi lng gia hai lncn cho ta bit khi lng H2O v CO2bhp th.

Nu trong thnh phn cht nghin cu c halogen, lu hunh, nit, chngc thto ra cc oxit ca nit, ca lu hunh, halogen v cc oxit halogen hydricv chng c thr nh hng n kt qucn cc ng hp th. loi trchng,trong ng nung phn cui, ngi ta dng cc si bc gihalogen v oxit luhunh, dng P2O5phn huoxit nit.2.2.1.2. Xc nh nit

xc nh s c mt ca nit trong hp cht nghin cu, ta c tht

nng mu thvi natri kim loi, nitcng cacbon trong mu thschuyn thnhNaCN, ho tan sn phm to thnh trong nc ct, lc ly dung dch; thm lnlt cc ion Fe2+, Fe3+, axit ho sto thnh kt ta mu xanh:

6CN- + Fe2+[Fe(CN)6]4-

4Fe3+ + 3[Fe(CN)6]4-Fe4[Fe(CN)6]3

mu xanhnh lng nit, ngi ta dng phng php Dumas hoc Kjeldahl.Nguyn l ca phng php Dumus l oxy ho hp cht hu cbng CuO

ri li cun sn phm bng mt dng CO2 tinh khit. Nit trong cht hu c schuyn thnh N2tdo. Ta c ththu N2thot ra bng mt buret p ngc trong


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chu cha dunh dch KOH m c. H2O sngng ttrong dunh dch; CO2honton bhp thbi KOH; N2thot ln c v ta c tho ch thtch ca n

mt cch ddng.Phng php Kjeldahl tuy khng phbin bng phng php Dumus songtrong nhiu trng hp cng rt thun tin, n cho php xc nh nhanh hmlng nit trong mu th. Bng cch v c ho hp cht nghin cu khi nungnng trong H2SO4m c c xc tc selen (khi cn c ththm cht oxy ho) tachuyn nitthnh mui amon sunfat, sau kim ho dung dch thu c ri licun NH3theo hi nc sang mt bnh khc v chun lng NH3to thnh.2.2.1.3. Xc nh halogen

Sc mt ca halogen trong hp cht hu cc xc nh bng cch tmmu giy vo si dy ng ri t, nu hp cht c cha halogen sto ra ngnla mu xanh lc.

Ngi ta nh lng halogen bng cch oxy ho mu cht trong bnh chaoxy nguyn cht, c xc tc Pt, khi s to halogen hydric, hp thbng dungdch HNO3v sau xc nh bng phn ng nitrat bc:

AgNO3+ HX AgX+ HNO3Bng cch so c hoc chun lng Ag+d, ngi ta tnh c hm

lng halogen trong mu cht nghin cu.2.2.1.4. Xc nh lu hunh

Khi un chy hp cht hu c vi kim loi, lu hunh s chuyn thnhNa2S, sau ta c thddng nhn bit c bng cch phn ng to kt ta PbShay Ag2S:

Pb(NO3)2+ Na2SPbS+ 2NaNO3nh lng lu hunh, ngi ta oxy ho mu cht hu cbng HNO3

bc khi trong ng hn kn 200 300oC, sau vi gilu hunh trong mu chtschuyn ho thnh H2SO4, ta c thnh bng phn ng viBaCl2, ri xc nhlng BaSO4bng phng php trng lng:

H2SO4+ BaCl2= BaSO4+ 2HCl

2.2.1.5. Xc nh cc nguyn tkhcNgoi cc nguyn tktrn, trong mt s trng hp chy hu cc th

cn cha P, Si, mt skim loi khc...Ta cng oxy ho hp cht hu cbng HNO3bc khi trong ng hn knhoc nung chy n vi hn hp NaNO3 v Na2CO3. Cc nguyn t ni trn schuyn ho thnh cc hp cht v c tng ng (thng vi ho tr dng caonht), sau ta nh lng chng bng cc phng php v cthng thng.2.2.1.6. Xc nh oxy

Hm lng oxy trong cc hp cht thng c xc nh mt cch gintip, tc l ta ly khi lng mu em t tri khi lng tng cc nguyn tva xc nh theo cc phng php trn, hoc ly 100% tri hp phn ca ccnguyn tkhc.


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Ta cng c thxc nh mt cch trc tip bng cch chuyn oxy trong hpcht hu cthnh CO ri oxy ho bng I2O5:

5CO +I2O5

5CO2+ I2Chun lng I2, CO2 c gii phng ra hoc chun lng I2O5d,ta tnh c lng CO hnh thnh.

Tm li, nhnhng phn tch chto cc kchnh xc, nhnhng thit bphn tch ngy cng hon thin, ngi ta c thtin hnh phn tch vi lng hocbn vi lng, vi nhng cht nh(vi mg) cng cho ta kt qung tin cy. Tnhng nm 60, ngi ta pht hin v sdng cc phng php siu vi lng,chcn cn mu cht (trn cn in ttng) cn cc sn phm t chy cxc nh bng nhng thit b tinh vi trn cso dn nhit ca cc cht khnhbpht in etect. Vi phng php ny, ngi ta c thxc nh ngthi C, H, N hon ton tng trong vng 10 pht, lng mu chcn khong 1mg.2.2.2. Thit lp cng thc tng qut ca hp cht

Sau khi xc nh thnh phn khi lng (hoc thnh phn trm khi lng)ca tng nguyn t trong cht nghin cu, bng cch chia cho nguyn t lngca cc nguyn t tng ng, ta sc t lgia snguyn t tng nguyn ttrong phn t, t thit lp c cng thc tng qut ca cc cht cho didng (CxHyOzNt)n

V d: t chy 1,5 mg mt cht A to thnh 0,9 mg H2O; 1,76 mg CO2v0,224 ml N2 (ktc). Ta tnh khi lng tng nguyn ttrong mu cht nhsau:0,9 mg H2O 0,0009/ 18 ptg (0,0009/18) x 2 = 0,0001g H = 0,1 mg H

1.76 mg CO20,00176/44 ptg (0,00176/44) x 12 = 0,00048 g C = 0,48 mg C0,224 ml N20,224/22,4 ptg (0,224/22,4) x 28 = 0,28 mg NLng oxy: mO= 1,5 -(0,48+0,1+0,28) = 0,64 mgTa c:

CxHyOzNt+ (x+y/4-z/2) O2xCO2+y/2 H2O + t/2 N2V x : y : z : t = 0,48/12 : 0,1/1 : 0,64/16 : 0,28/14 = 2 : 5 : 2 : 1

Vy cng thc tng qut ca cht nghin cu l (C2H5O2N)n.xc nh n ta phi xc nh khi lng phn tcht cho hoc i khi

khng thc hin c trong iu kin th phi bin lun.2.2.3. Xc nh khi lng phn tca mt cht

tm c cng thc nguyn (cng thc phn t) ca mt hp cht, taphi xc nh khi lng phn t, hay ni chnh xc hn l xc nh phn tgamca cht nghin cu. C nhiu phng php xc nh phn tlng.

a. Nu mu cht nghin cu l cht lng dbay hi, ta cho bay hi nhit thch hp, o th tch hi iu kin ri tnh phn t lng ca n theophng trnh:

pV = nRT = (m/M)RTptg: M = mRT/pV

Trong :p - p sut;


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V - thtch hi cht nghin cu;m - khi lng cht bay hi;

T - nhit tuyt i;R - hng skh.b. Nu o c tkhi hi ca cht cho i vi mt cht kh no , ta

c thtnh c phn tgam ca n mt cch ddng.V d, hi cht A nng gp 25 ln H2th phn tlng ca n phi l

M = 25 x 2 = 50.c. Da vo nh lut RaoultDung dch mt cht kh bay hi trong mt dung mi no c lun c

nhit si cao hn, nhit ng c thp hn so vi dung mi nguyn cht vtng im si hay him kt tinh lun tlvi nng cht tan.

t = KCK - hstl, c gi l hng snghim si hay nghim lnh, c trng

cho tng loai dung mi;C - nng mol/l hay ptg/1000 g dung miBng cch o mc tng nhit si (phng php nghim si) hoc mc

him kt tinh (phng php nghim lnh) ca dung dch cht nghin cu trongdung mi cht thch hp, ta ddng xc nh c nng cht tan v do xcnh c phn tgam ca chng.

Ngi ta hay dng campho lm dung mi, v hng snghim lnh ca nkh cao (khi ho tan mt phn tgam cht tan trong 1000 g campho, im ngc hi t =37,7oC.

d. Cc phng php khcBng cch tng t, ngi ta cng c tho p sut thm thu ca dung

dch cht tan, o nht ca dung dch hoc bng phng php khi ph, txc nh c khi lng phn t cht cho. Nu bit r snhm chc trongmt phn tcht nghin cu, bng cch xc nh snhm chc cng cho php xnh phn tlng ca chng.

V d, 0,92 g mt alcol n chc tc dng vi mt lng dNa cho 0,224 lH2(ktc) th phn tlng ca alcol phi l:

0,92/ (0,224 x 2)/22,4 = 462.2.4. Thit lp cng thc nguyn ca mt hp cht

Sau khi xc nh c cng thc tng qut ca cht nghin cu khi lngphn tca n, ta ddng tm ra c tr sca n v do thit lp cng thcnguyn ca hp cht.

V d, lp c cng thc tng qut ca cht A di dng (C2H5O2N)nnhv dtrn, ng thi bng mt trong cc phng php va nu ta xc nhc phn tlng ca cht A l 75, ta tnh c:

(2 x 12+5 x 1+2 x 16+1 x 14)n = 7575n = 75 n = 1Vy cng thc nguyn ca A phi l C2H5O2N.


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Tuy vy, nhiu khi trong iu kin thc nghim khng cho php ta thchin tt ccc bc trn, c ngha l phi gii bi ton tm cng thc nguyn khi

s phng trnh ton hc lp c it hn sn s, trong khi trng hp ny taphi bin lun. Phng php bin lun phi da vo c im ca hp cht choxc nh trsn trong cng thc tng qut, hoc da vo cc bt phng trnhphn nh mi tng quan gia snguyeen tca cc nguyn tcbn.

V d, mt hydrocacbon c tkhi i vi hydro l 21. Hy tm cng thcca n.

Ta c khi lng phn tl 21x2 = 42. Nu gi cng thc ca hydrocacbon l CxHy, ta c:

12x + y = 42Suy ra: 12x < 42Hay : x < 3,5

Mt khc CxHy l hydrocacbon nn s nguyn tH trong phn t khngvt qu 2x + 2, ngha l:

y 2x + 242-12x 2x + 2

40 14x2,8 x

Kt hp vi lp lun trn, ta c 2,8 x


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- ng phn vvtr ca nhm chc. Cc hp cht ny c cng nhm chc nhngkhc nhau vsphn bvtr ca nhm chc:

CH3CHCH

2CH

3

OH

CH3CH

2CH

2CH

2OH

2-Butanol 1-Butanol - ng phn vnhm chc:

CH3CH2CH2CH2OHCH3CH2-O-CH3

ete ancol - ng phn vcch chia on mch ca nhm chc:

CH3C-O-CH2CH2CH3

O

CH3-O-C-CH2CH2CH3

O

axetat n - propyl butyrat metyl Hai cht u thuc este, nhng xut pht thai cp axit v ancol khc nhau,

axetat n - propyl hnh thnh t CH3COOH + CH3CH2CH2OH, cn este butyratmetyl hnh thnh tCH3CH2CH2COOH + CH3OH.b. ng phn hnh hc* Khi nim: L ng phn cu hnh do ssp xp khc nhau ca cc nhm th2 bn ni i hay mt phng vng no. Ssp xp cc nhm thhai bn ni ithc cht l hai bn mt phng . Mt phng v mt phng vng l nhng mt

phng cnh.Nu hai nhm th ging nhau hay gn ging nhau cng pha ca mtphng gi l ng phncis, khc pha l ng phn trans.

V d:

C C

CH3

HH

H3C

C C

H

CH3H

H3C

cis-2-butentrans-2-buten

Cl

H

H

Cl

H

H

H

Cl

H

Cl

H

H

cis-diclopropan trans-diclopropan


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Cch qui nh vtr hai nhm thging nhau trn y chl trng hp cbit trong cch qui nh tng qut vv tr ca 2 nhm th trong mch chnh, v

d:CH3 > H

C2H5 > CH3C C

C2H5

HH

H3C

C C

CH3

C2H5H

H3C

*iu kin cn v xut hin ng phn hnh hciu kin cn: Phn tphi c ni i hay vng no nm trn mt mt phng.iu kin : 2 nhm th mi cacbon ni i hay vng no phi khcnhau.

C C

c

d

a

b * Phn loi: c 3 loi- ng phn cis - trans- ng phn syn - anti- ng phn E - Z

Trong trng hp khng dng c danh php cis - trans th dng danhphp chung gi l danh php E-Z.

Danh php E-Z da trn tnh hn cp ca nguyn tnh vi cacbon. Nhm

th c nguyn t c s th t nguyn tcao hn (hay c khi lng nguyn thoc phn tln hn) th c tnh hn cp cao hn. Nu hai nhm thc tnh hncp cng pha ca mt phng gi l ng phn Z, khc pha l ng phn E.

V d:

C C

NO2

H

Br

H3C

C C

H

NO2

Br

H3C

Br > CH3 , NO2 > H

(Z)-2-Brom-1-nitropropen (E)-2-Brom-1-nitropropen

Danh php Syn-anti: Dng cho ni i

C Y

c mt cp in tkhng phn chia. (syn-: cng pha, anti-: khc pha).

a b

c d

..


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V d: CH3- CH = N - OH

C N

OH

H

H3C

C N

H

H3C

OH

Syn- anti-

* Tnh cht khc nhau ca ng phn hnh hcCc ng phn hnh hc c nhiu tnh cht khc nhau r rt, v d1,2-

icloetilen.cis trans

Khong cch 2 Cl 3,7A0 4,7A0 1,89D 0,0Dt0nc -80,50C -500Ct0s 600C 480C

* ngha: Gii thch ti sao c 2 nguyn tcacbon v hidro m to nn v sccphn thp cht hu c.c. ng phn khng gian*ng phn quang hca, Khi nim: Nhng hp cht c cu trc v tnh cht vt l, ho hc ging nhau

nhng khc nhau vkhnng quay mt phng nh sng phn cc gi l ng phnquang hc.

nh sng l dao ng sng ca trng in v t. Khi mt electron tngtc vi nh sng th c dao ng theo tn sca nh sng theo hng ca trngin. nh sng thng c vect trng in ca sng nh sng trong tt c cchng ca mt phng. nh sng phn cc c vectca trng in ca tt cccsng nh sng trong cng mt mt phng, gi l mt phng phn cc.

nh sng phn cc thu c khi cho nh sng thng i qua lng knhphn cc:

nh sng thng nh sng phn cc

nh sng thng nh sng phn cc

Phn cc k


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C mt scht hu c(v cmt scht v c) c khnng lm quay mtphng phn cc khi cho nh sng phn cc i qua. Khnng gi l tnh quanghot, cn nhng cht c khnng gi l cht quang hot. Trong snhng chtquang hot c mt skhng nhiu lm chthhin khnng lm quay mt phngphn cc khi cn trng thi tinh th(tinh thbt i), v d: tinh thca cc chtNaCl, ZnSO4. Cn mt sln cht khc li c tnh quang hot khi thhi haytrong dung dch. loi cht quang hot va ni, tnh quang hot khng phi docu trc tinh thm do cu trc ca nhng phn tring r.

o khnng lm quay mt phng phn cc (quay cc) ca cc cht

quang hot ngi ta dng phn cc k ghi ly gc quay . i vi mt chtquang hot ngi ta thng dng i lng quay cc ring []. quay ccring ca mt cht trong dung dch c tnh theo cng thc sau:

[ ]aL

Vt.

.0 =

Trong :: Gc quay quan st c i vi mt dung dch c bdy nh sng i qua ld (dm) cha a (g) cht quang hot trong V (ml) dung dch. Vic thc hin t0,

vi nh sng c di sng .Gc quay ca mt cht quang hot khng nhng ph thuc vo bn cht

ho hc ca cht , bc sng ca nh sng phn cc, bdy ca dung dch chtquang hot, nhit khi o, m cn phthuc vo nng v bn cht dung mi.Cho nn khi vit quay cc ring phi gi cth. V d:

[ ] 025 18=D (C = 15 nc)Nhthc ngha l quay cc ring ca cht quay vbn tri 180, nng

15g trong 100 ml dung dch nc, nhit khi o l 250, b dy dung dch1dm, nh sng c dng l nh sng D ca natri vi bc sng 589nm.


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b,iu kin xut hin ng phn quang hciu kin cn: Phi c trung tm bt i (Nguyn tbt i, phn tbt i hay

tinh thbt i)- iu kin : Phi c phn btheo cng thc chiu Fis.iu kin cn v xut hin tnh quang hot l khi phn chiu m

hnh ca hp cht qua mt mt phng ta c m hnh khc khng ng nht vin, ngha l khng thchbng chuyn ng tnh tin v quay m c tha chai m hnh lng kht vo nhau c. Ni cch khc, xut hin c hintng quang hot, phn tphi khng lng kht c vi nh gng ca n, tngtnhquan hgia hai bn tay ca mt ngi bnh thng. Tnh cht c gil tnh khng trng vt - nh(chirality). Khi c hin tng khng trng vt - nh,sxut hin hai dng ng phn i xng nhau, khng lng kht vo nhau cnhhnh a.1

Hnh a.1: Hai dng ng phn i xng nhauHai ng phn ny c khnng lm quay mt phng nh sng phn cc

nhng gc c tr snhnhau nhng theo chiu ngc nhau. l hai cht iquang.Nguyn tcacbon bt i

Trong mt hnh tdin u c mt tm i xng, bn trc i xng v sumt phng i xng.

Nu ta thay th tt c bn nguyn t hydro trong phn t CH4 bng bn

nguyn thay nhm nguyn t ging ht nhau th cc yu ti xng vn cnnguyn vn. Nhng nu thay thmt hay nhiu nguyn thydro trong CH4bngnhng nguyn thay nhm nguyn tkhc nhau th cc yu ti xng sbviphm. V d: Thmt nguyn tH bng Br th chcn mt trc i xng v bamt phng i xng, th3 nguyn tH bng 3 nguyn tkhc nhau th skhngcn mt yu ti xng no c.

Khi trong phn tc nguyn tC nh vi 4 nguyn thay nhm nguynt khc nhau Cabcd s xut hin hai dng ng phn i xng nhau qua mtphng nhvt vi nh trong gung (hnh a.1) v c tnh quang hot. Nguyn tCgi l nguyn tC bt i, phn tCabcd l phn tbt i.

a

dc

b

a

cd

Mt phng gng


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25

V d:

C*

a

b

c

d C*

H

H3C

OH

COOH C*

H

Cl

I

SO3H C*

F

Cl

Br

I

Trong trng hp hai nguyn tng vnh vo mt nguyn tC cng

vi hai nhm nguyn t khc na, nguyn t C cng l C bt i, cho nnnhng hp cht nhtrong v ddi y cng c thl nhng cht quang hot:

C*

H

C6H5

D

CH3 C*

H

H3C

OH

CD3

biu din nguyn tcacbon tdin trong cc phn tkiu Cabcd ta c

thdng cc cng thc khc nhau hnh a.2. l cc cng thc tdin (1), Fis(2) v (3), phi cnh (4) v phi cnh kt hp vi Fis(5). Trong cc cng thc, nt lin biu din lin kt nm trn mt phng giy, nhng ng chm nhhoc ng gch ngn dn dng chnhng lin kt hay ng ni hng vpha di mt phng giy (i xa pha ngi quan st), cn cc ng m hnhtam gic chnhng lin kt hng tmt phng giy vpha ngi quan st (ign pha ngi quan st) :

b

d

c

a

c

a

d

b

c

a

d

b

(1) (2) (3)


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26

c

ab

d

a

c

b

d

(4) (5)

Quy tc chiu FisMch chnh biu din cnh nm dc.Nguyn thoc nhm nguyn tc soxi ho cao th c biu din phatrn, ngc li th biu din pha di. Qui c: Cc nhm nguyn tng k ngang (a v b) pha gn ngiquan st, cn cc nhm nguyn tng dc (c v d) pha xa hn. Munchuyn cng thc hnh tdin sang cng thc Fista dng phng php chiu ccnhm nguyn tca tdin ln mt phng giy. Khi y cn ch l tdin phic phn b nh th no mt cnh nm ngang ca t din gn ngiquan st:

V d: CH3 CHOH*

CHO

+1-3

Ta c th bin i cng thc Fis theo cc cch khc nhau, khi y tu tngtrng hp m cu hnh vn c bo ton hay bnghch o (quay cu hnh).

i chbt khai nhm thno C cng lm quay cu hnh v nhvyssinh ra mt dng khc ca phn tban u.

CHO

CH3

OHH

CHO

CH3

HOH

b

d

c

a

c

a b

d

c

a b

d


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27

V d:

Nu dch chuyn ng thi ba nhm th theo chiu kim ng h hoctheo chiu ngc li th cng thc Fisvn ginguyn ngha, tc l cu hnhc bo ton.V d:

CHO

CH2OH

H OH

Dng D

Khng c a cng thc Fis ra khi mt phng giy, cng khngc quay cng thc trn mt phng nhng gc 900hay 2700(v squay cu hnh)nhng c thquay 1800(cu hnh khng i).V d:

CHO

CH2OH

H OH

Dng D

CHO

CH2OH

H OH

Dng D

CHO

CH2OH

OH H

Dng L

OH

CH2OH

OCH H

Dng D

CHO

H

OH CH2OH

Dng D

Quay 90

H

CHOHOCH2

OH

CHO

HHO

CH2OH

Dng L

CHO

CH2OH

OHH

Dng D

Quay 1800

CH2OH

CHO

HO

Dng D

H


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28

biu din hai hay nhiu nguyn tcacbon tdin k tip nhau ta cng cdng cng thc tdin hay cng thc FisV d: Vit ng phn quang hc ca : HOOC-CHOH-CHOH-COOH

c. Phn loi ng phn quang hcCp i quang: V d: Andehit glixeric HOCH2-CHOH-CH=O

Tnh cht ca mt cp i quangGing nhau: Hai cht i quang c cc tnh cht vt l v ho hc bnh

thng ging ht nhau. Khc nhau: Chng khc nhau du ca nng sut quay cc ( = +:

quay sang phi; = - : quay sang tri) v hot tnh sinh hc (tng tc vi tcnhn c tnh quang hot). Nhng skhc nhau ny bt ngun tskhc nhau vcu hnh.

CHO

CH2OH

H OH

Andehit D (+) glixeric

CHO

CH2OH

OH H

Andehit L (-) glixeric

COOH

COOH

H

H

OH

OH

COOH

COOH

HO

HO

H

H

COOH

COOH

H

HO

OH

H

COOH

COOH

HO

H

H

OH

ng phn mz Hai ng phn i quang

Hai ng phn khng i quang


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29

Cp khng i quang (ng phn lp thia): Tnh cht ca cp ngphn quang hc khng i quang

Ging nhau: C tnh cht vt l v ho hc bnh thng ging ht nhau.Khc nhau: Gi tr gc quay cc khc nhau nhng c th giing nhau

hoc khc nhau vdu.ng phn mz

L ng phn c yu ti xng ni phn t, c c im gc quay ccring = 0. L ng phn lp thkhng quang hot (do sb trni phn t).V d:

Bin thRaxmic

V d:

Thng thng trong tnhin cng nhtrong cc qu trnh hc hc, ngita hay gp hai cht i quang ca mt cht tn ti dng tp hp ng phn t

(cu to ca tp hp cha tht r rng) gi l bin thraxmic. K hiu bng du( ) hay chD, L hoc d, l. V d: andehyt ( ) glyxric. Tt nhin phi hiu rngkhi nim bin thraxmic l mt khi nim c tch cch thng k, khng dng chcc phn tring rm chmt tp hp ln cc phn t.

Bin thraxmic khng c tnh quang hot v y c sb trnhau vnng sut quay cc gia hai cht i quang (= 0).

Thng thng cc trng thi kh, lng hay dung dch, bin thraxmic cthc coi l hn hp ng phn tgn nhl tng ca hai cht i quang chonn n c tnh cht vt l ging nhcc cht i quang to nn n nht0s, tkhi,chit sut, quang phhng ngoi trng thi lng hay dung dch,...

COOH

COOH

H

H

OH

OH

COOH

COOH

HO

HO

H

H

Axit mztactric

CN

CH3

OHH

CN

CH3

HHO


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30

Ch : H thng k hiu D-L c nhng hn ch nht nh nn hin nayngi ta dng phbin hthng R-S chcu hnh........

S ng phn quang hc ca mt hp cht l: N = 2

n

trong n l snguyn tC bt i. Tuy nhin i vi cc cht c si xng ring trong phn tth sng phn lp tht hn 2n.* ng phn cu dnga. Khi nim- Cu dng l nhng dng cu trc khng gian sinh ra do squay xung quanh mthay vi lin kt n m khng lm t nhng lin kt ny.- ng phn cu dng (ng phn quay) l nhng cu dng tng i bn caphn t.b. iu kin c ng phn cu dngiu kin cn: C lin kt n C - C.iu kin : Phi c m t bng cng thc Niumen hoc biu din didng phi cnh.c. Phn loiCu dng ca etan v cc hp cht kiu X3C - CX3

Dng che khut: Dng c thnng cao nht, cu dng ny khng bn.

H

H

H

H

H

HH

H

H

H

HH

Dng xen k: Dng c thnng thp nht, cu dng ny bn.

H

H

H

H

H

H

H

H

H

HH

H

Sng phn cu dng: N =n

0360vi n l gc quay. Nhvy ta sc

v vn dng hnh hc khc nhau, trong c hai dng ti hn l dng che khut vdng xen k.


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31

Biu din thnng theo gc nhdin ( n = 600) ta sc gin thnng:

H

H

H

H

HH

H H

H

H

HH H

H

H

H

HH

H H

H

H

HH

H

H

H

H

HH

H H

H

H

HH

H

H

H

H

HH

Gin trn c dng hnh syn, vi 3 cc i bng nhau v 3 cc tiu bng

nhau ng vi chnh lch vnng lng l 2,8 kcal/mol.Cu dng v gin thnng ca cc hp cht khc kiu X3C - CX3tng

tetan.

Butan v cc hp cht kiu XCH2 CH2Yi vi phn tn-butan CH3-CH2-CH2-CH3khi quanh quanh lin kt C-C

xut hin 2 cc i nng lng ng vi hai dng che khut: che khut ton phnv che khut 1 phn v 2 loi cc tiu nng lng ng vi 2 dng xen k. Ngi taphn bit 2 dng xen k: anti (hay transoit) v syn (cisoit). Dng anti tng ibn hn dng syn, chnh lch nhau khong 0,7 kcal/mol. Tng tc gia 2 nhmCH3- lm cho dng syn km bn, gi l tng tc syn. nhit thng, dnganti chim tlgp i dng syn.

i vi dn xut 1,2-dihalogen ca etan nh: 1,2-diclo etan; 1,2-dibrometan.Ta cng thy hin tng tng t nh n-butan. Kt qu nghin cu chothy rng trong dung dch CCl425

0C, 1,2-diclo etan tn ti ti 70% dng anti

0 60 120 300180 240 360Gc quay

E (kcal/mol)

1

2

3

CH3

CH3

H

H

H

H

CH3

CH3

H

H

H

HDng syn

Dn anti


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32

v 30% dng syn. Trong iu kin tng t1,2-dibrom etan cha 89% dng antiv 11% dng syn. Nu dng syn ca XCH2-CH2Y c lin kt hidro th skhc

thm ch dng syn bn hn dng anti.Cc cu dng tng i bn ca mt cht l nhng ng phn cu dng canhau.Cu dng ca hp cht khng no

Trong phn t nhng hp cht loi ny nguyn t hoc nhm nguyn tmang ni i thng vtr che khut i vi nguyn tH hay cc nhm thnhCl, CH3

Cu dng bn ca mt sphn tc ni ing ch l cc hp cht c 2 ni i lin hp nh: butadien-1,3; 1,3-

dicrolein c hai dng thng bn chkhc nhau vvtr nhm cha no so vi nin gia. V c s tng tvi ng phn hnh hc nn y ngi ta phnbit nhng dng l -cis v -trans. i vi butadien-1,3, dng s-trans bnhn dng s-cis l 2,3 kcal/mol

Cu dng ca cc hp cht vng no1. Nhng yu tlm gim bn v bin dng vng no

a. Sc cng Baye: (1885) l sc p hoc trng gc ho tr CCC so vigc ho tbnh thng 109028. Sc cng cng ln th vng cng km bn. Mc

sc cng l na hiu sgia gc ho trca vng phng v gc ho trbnhthng, tc l sai lch ca gc ho trtiu chun.

n (snguyn tcacbon ca vng) 3 4 5 6 7( sai lch vgc) 24064 9044 -5016 -9033 -12046

Nhth, theo cc trsc trng cho sc cng Baye th vng no bn nhtl xiclopentan cn nhng vng no km bn l xiclopropan v nhng vng ln.

Tuy vy, nhng ti liu tch lucho n nay cho rng kt lun ca Baye chp dng ng cho nhng vng 5 cnh tr xung m thi. Ngi ta tng hpnhng vng ln thy rng: nhng vng ny c bit l xiclohexan c bn ln

Axit fomic Etyl fomiat Metyl vinylete

C C

CH2 CH2

H H

C C

CH2

HCH2

H

-cis -trans

C

O

H

O

H

C

O

H

O

CH3

C

H2C

H

O

CH3


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33

hn dkin ca Baye nhiu. Xt theo thiu nhit tnh cho mt n v mt xchCH2ca vng trong bng sau:

n H H-157,4 n H H-157,42* 168,7 11,3 9 158,8 1,43 166,6 9,2 10 158,6 1,24 164,0 6,5 11 157,4 15 158,7 1,3 12 157,7 0,36 157,4 0 13 157,4 07 158,3 0,9 16 157,5 0,18 158,6 1,2 17 157,2 0,2

Ngi ta cng thy nng lng ca cc vng ln txiclopentan trln unhnhau, m theo quan im ca Baye th nng lng phi tng theo scnh ca

vng. b. Sc cng Pitz: Thc ra cc vng no (tr xiclopropan) khng phi lvng phng. Trong mt vng, ngoi sc cng Baye cn c sc cng do chccnguyn tH trng thi che khut mt phn hay ton phn gy nn. Do , mtvi nguyn tca vng b lch ra khi mt phng ca vng. Sc cng gi lsc cng Pitze.2. Cu dng ca cc vng no

a. Xiclopropan chc th trn mt mt phng. Cc nguyn tH trngthi che khut. Cn cc lin kt C-C bbin dng. Do vng ny t bn.

b. Xiclobutan chc thtrn mt phng ca 3 nguyn tcn li. iu nyc xc nh bi cc kt qunghin cu quang phcng nhphng php nhiuxelectron.

c. Trong xiclopentan hu nhkhng c sc cng gc nhng sc y li ln.Do trong trng thi bn ca xiclopentan c mt nguyn tC bchch ra khi

mt phng ca vng 0,5o

A :

d. Cu dng ca xiclohexan:d1: Hnh dng ca vng xiclohexan

Xiclohexan cng c cu trc khng phng. m bo cho gc ho trbnh thng, xiclohexan cng c nhiu dng khc nhau: dng thuyn, dng xon,dng gh:

H

H

H

H

H H

H

H

H

H

H

H

H

H

xiclobutan xiclopentan

HH

H

H

H

H

HH

H

H

xiclopropan


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34

1

2

1

34

6

5

Trn cc dng trn, dng gh l dng bn v vy tuyt ai a s cc hpcht c vng xiclohexan cc phn t tn ti hu nhchdng gh. nhit phng, trong xiclohexan c ti 99,9% phn ttn ti dng gh.

Hai dng ng ch hn c l dng gh v dng thuyn.C 2 dng nykhng c sc cng Baye v cc gc ho trca cacbon u bnh thng (109028).dng ghkhng c sc cng Pitze nn bn hn dng thuyn.

Tht vy, ta c thcoi phn txiclohexan nhthp ca 6 hthng C-Cging n-butan. dng ghtt c6 hthng ny u theo cu dng xen ktngtsyn-butan qung cch gia cc nt H 2 nt C knhau hay khng knhau uln.

Trong khi , dng thuyn chc 4 hthng: C1-C2; C3-C4; C4-C5; C6-C1c cu dng xen kcn 2 hthng cn li (C2-C3, C5-C6) c cu dng che khuttng t cu dng che khut ca n-butan. Khng nhng th khong cch cc nt

C2-C4chcch nhau 1,810

A (so vi tng bn knh VanderWalls 2,40

A ) nn chngy nhau, kt qudng thuyn km bn hn dng ghkhong 7 kcal/mol.

H

CH3 H

H

HCH3 CH3

H

H

H

H

CH3

dng ghso snh vi cp syn-butan

H

H

H

HH

H

H

H

H

H

2,490

A

2

3

4

6


35/111

35

a e

Cu dng ghca xiclohexan tn ti gia trng thi cn bng gia 2 dngkhc nhau:

Qa trnh chuyn ho xy ra rt nhanh (106ln/s) phi i qua nhng dngkm bn l dng na gh, dng thuyn v dng xon. Dng xon bn hn dngthuyn khong 1,4 kcal/mol, cn dng na ghkm bn nht (km dng thuyn 4kcal/mol)

d2: Lin kt trc v lin kt bindng gh6 nt cacbon c phn btrn hai mt phng song song v cch

nhau 0,50

A ( mi mt phng cha 3 nt cacbon vtr lun phin nhau. Trc ixng bc ba ca nt thng gc vi mt phng . Su lin kt C-C song song vitrc i xng c gi l lin kt trc, k hiu a; cn su lin kt C-C hng rangoi bin ca phn tv to vi trc i xng nhng gc 109028, gi l lin ktbin, k hiu e

e. Dn xut thca xiclohexanV c 2 kiu lin kt a v e nn cc dn xut thmt ln ca xiclohexan

c 2 cu dng: dng a v dng e.

H

H

H

HH

H

H

H

H

HH

H

H

H

H

HH

H

H

H

H

HH

H

CH3

CH3

2

3

4

6

Cc lin kt a v e trong xiclohexan (a: axial; e: equatorial)

a

a

a

a

a

a

e

e

e

e

e

e

e

e

e

e

e

e

a

a

a

a

a

a


36/111

36

Hai dng a v e chuyn ho vi nhau rt nhanh nn khng th tch ring

chng vi nhau c, sc mt chng trong cn bng trn c chng minhbng phng php vt l. Kt qukho st l thuyt v thc nghim cho thy rngcu to dng e bn hn dng a khong 1,7 kcal/mol. nhit phng, e-metylxiclohexan chim 95%, cn dng a-metylxiclohexan chim 5% trong hnhp cn bng.

Skm bn ca cu dng a so vi dng e do c tng tc syn gia nhmthCH3vi C6, mt khc nhm thCH3tng tc y vi C3v C5. (nhm nhmthe khng gy hin tng ny)

Tng tc syn khng nhng a-metylxiclohexan m cn thy cc dngaxial mt ln thkhc na. Tutheo bn cht v kch thc ca nhm thX trongxiclohexan m schnh lch vnng lng ca cu dng a v e khc nhau.

i vi dn xut th2 ln ca xiclohexan, 2 nhm thc thvtr 1,1;1,2; 1,3 hoc 1,4. Trong trng hp dn xut th1,1, nu 2 nhm thng nht thchc mt dng gh. Nu 2 nhm thkhng ng nht sc 2 cu dng gh, trong c mt cu dng u tin l cu dng c nhm thln vtr e. V d:

Cc cu dng 1,2; 1,3; 1,4 c thtn ti dng cis-trans. ng phn cis-1,2c nhm th phn btheo kiu a,e hoc e,a cn ng phn trans-1,2 hai nhm thl a,a hoc e,e.

a

e

CH

CH

2

3

4

6

2

3

4

6

Tng tc syn

Tng tc anti

CH3

C2H5CH3

F


37/111

37

Hai cu dng cis-1,2 (a,e) v (e,a) l ng nht nu 2 nhm R l ng nht.Cu dng ny c 3 tng tc syn lm gim bn l: R-C1-C2-R; R-C1-C6-C5;v R-C2-C3-C4. Cu dng trans-1,2 (a,a) c 4 tng tc syn cc h: R-C1-C2-C3;R-C1-C6-C5; R-C2-C6-C4. Trong khi , cu dng trans-1,2 (e,e) chc mt tngtc hR-C1-C2-R, v vy cu dng ny bn hn c. nhit phng, trans-1,2-dimetylxiclohexan tn ti dng e ti 99%.

ng phn cis ca cc dn xut 1,3 hai ln thgm 2 dng a,a v e,e cnng phn trans tn ti di dng a,e v e,a (hai cu dng ny l ng nht vi 2nhm thl ng nht).

S tng tc syn mi cu dng l cis-1,3 (a,a) l 2; cis-1,3 (e,e) l 0;trans-1,3 (e,a) hoc trans-1,3 (a,e) l 2. V vy, cis-1,3 (e,e) l cu dng bn nht.

Quan hcu dng ca cc dn xut 2 ln th: ng phn trans-1,4 c 2 cudng a,a (4 tng tc syn) v e,e khng c tng tc syn, bn nht; ng phn cis-1,4 c thl a,e hoc e,a (2 tng tc syn).

cis-1,2

trans-1,2

R

R

R

R

R

R

1

2

1

2

1

2

3

3 3

4

4

4

5

55

6 6

6

R

R

R

R

R

R

1

23

4

5 6 1

2

3

4

56

1

2

34

5

6

R

R 1

32

4

5 6

R

R

1

3

2

4

5

6

R

R 13

2

4

5

6

cis-1,3

RR

13

2

4

5

6 R

R

1

3

2

4

5

6R

R

1

3

2

4

5 6

trans-1,3


38/111

38

Trong nhng trng hp c 2 nhm R khng ng nht cc dn xut 1,4cng nhdn xut 2 ln thkhc, cc cn bng gia 2 cu dng a,e hoc e,a s

lch vpha cu dng no c nhm thc kch thc ln vtr e.Trong nhng dn xut 6 ln th 6 cacbon khc nhau ca xiclohexanC6H6X6 ng ch hn c l hexacloxiclohexxan (X=Cl),hexahidroxylxiclohexxan (inozit-X=OH). Nhng dn xut c thc 8 cu dngkhc nhau:

Trong , c mt cu dng l bin thraxemic d,l. Mi cu dng c k hiuring bng ch ci Hi-Lp (cho C6H6Cl6) hoc ch ci La-tinh (cho inozitC6H6(OH)6)

g. Cu dng tetrahidropiranTng txiclohexan, dng ghtetrahidropiran l dng bn. V c dtoxi

nn c 2 dng gh1C v C1 ( C: chair); chng trng thi cn bng v i xngnhau qua mt phng gng:

O O O

C1 1C

cis ( )

pi () allo ()

muco ( ) neo ()Sillo ()

milo ( )

d,l-()

(-)(+)


39/111

39

Cc hexpiranozo C6H12O6 c 16 ng phn quang hc mi ng phnquang hc mi ng phn c thtn ti dng hay . Mi dng anome ny

li c hai dng bn l C1 v 1C. Th d-glucopinarozo gm 2 dng 1C v C1nhsau:

i vi phn ln cc dng pinarozo dng C1 bn hn 1C. C nhiu yu tlm monosaccarit chuyn tdng ny sang dng khc gi l cc yu tkhng bn. l sc mt ca nhm OH axial, nhm CH2OH axial v nhm OH axial cngpha (hiu ng Hatxenotta); nhm OH axial C2 (hiu ng delta 2) nhm OHequatorial C1( hiu ng anome).....

2.3.2.ng ng2.3.2.1. Khi nim

Nhng hp cht c tnh cht vt l v ho hc gn ging nhau nhng khcnhau mt hay nhiu nhm metylen (-CH2-) nm trong mt dy ng ng. Nhngcht nm trong dy gi l cht ng ng. Mt dy ng ng c CTTQ chung.

2.3.2.2. Tnh chtCc hp cht trong dy ng ng c tnh cht vt l nhnhit si, nhit

nng chy tng khi tng snhm metylen, ngha l tng khi lng phn tdotng thm chiu di mch cacbon.

Khi nim ng ng thng dng don sthay i tnh cht vt lkhi thay i thnh phn nhm metylen.

Cc cht trong dy ng ng cn phi c cng cu trc mch cacbon.V d: CH3CH2CH2CH3v CH3CH2CH2CH2CH3l hai ng ng ca nhau.

(CH3)2CHCH3v (CH3)2CHCH2CH3l hai ng ng ca nhau.CH3CH2CH2CH3 v (CH3)2CHCH2CH3khng phi l ng ng ca nhau

m nm trong hai dy ng ng n - ankan v isoankan.Hin nay, thng chni n dy ng ng ca metan, etylen, axetylen vnhng dy ng ng cuae ancol metylic, andehit fomic, axit fomic,...ngha lnhng hp cht c mch cacbon khng nhnh nhn-ankan, n-anken, n-ankin hayn-ancol, n-axit,...

2.3.3.ng cp2.3.3.1. Khi nim: L nhng hp cht c cng snguyn tcacbon nhng khcnhau mt bi 2n nguyn thidro.V d: CHCH, CH2=CH2, CH3-CH3: ng cp2.3.3.2. Phn loi

O

OH

CH2OH

OH

OH

OH

O

OH

OH

OH

OH

H2COH

C11C


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* Cng vtr lin ktV d: CH3-CH2-CH2-CH3 , CH2=CH-CH2-CH3, CHC-CH2-CH3

* Khng cng vtr lin ktV d: CH2=CH-CH2-CH3, CH2-CCH-CH32.3.4. Cu hnh2.3.4.1. Khi nim: L mt squi c t c thbit c cch thc phn bca cc nguyn thoc nhm nguyn tca mt phn ttrong khng gian.2.3.4.2. Phn loiCu hnh hnh hcCu hnh quang hcCu hnh cu dng2.3.4.3. Cu hnh hnh hc gm 3 loi:Cu hnh cis-transCu hnh syn-antiCu hnh E-Z2.3.4.4. Cu hnh quang hc gm 2 loi:Cu hnh D-L

xt cu hnh D, L phi c nguyn t cacbon bt i v phi biu dincng thc cu to ca n di dng Fis.

Nu nguyn thoc nhm nguyn td tca nguyn tC*nm vphabn phi th l cu hnh D v ngc li.

V d: CHO - CH2OH - CH2OH

Trong trng hp nhiu nguyn t C*, xt nguyn t C* no nm gnnguyn tC c soxi ho thp nht.

V d: HOOC - CHCl - CHOH - CH3

CHO

CH2OH

H OH

Andehit D (+) glixeric

CHO

CH2OH

OH H

Andehit L (-) glixeric

COOH

H ClH OH

CH3

HOCl H

H

COOH

CH3

COOH

CH3 CH3

COOH

Cl HH OH

H ClHO H

D DL L


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Cu hnh R-S: Do 3 nh bc hc pht minh ra l: Cahn - Ingold - Prelog.Cu hnh R-S c xc nh theo tnh hn cp ca trung tm chiral (C*)

theo thta > b > c > d, chyu cn cvo stht(hoc khi lng nguynt) ca cc nguyn tni vi C*.V d: Br > Cl > SH > OH > NH2> CH3> H

OH > COOH > CHO > CH2OH > CH3Nu cc nguyn t ni trc tip vi C* l ng nht th cn xt thm

nguyn ttip theo, khi y cn ch nhn i hoc ba i vi nguyn tmang nii hoc ni ba.

Biu din cng thc di dng cng thc phi cnh: t tdin sao cholin kt vi nguyn t hoc nhm nguyn t tr nht (cp nh nht) i xa phangi quan st th thtphn bba nhm thcn li snm trn mt mt phngpha gn ngi quan st sxc nh cu hnh. Nu sgim tnh hn cp ca ccnhm th theo chiu kim ng hth trung tm chiral c cu hnh R (rectus -quay phi), nu theo chiu ngc kim ng h th trung tm c cu hnh S(sinister - quay tri).

c

b

ad

c

d

ab

R S CH2OH

CHO

OH

HOH2C

H

HOCHO

ANDEHIT R-GLIXERIC ANDEHIT S-GLIXERIC

H

C thhnh dung cc nhm tha, b, c to nn hnh tam gic v nhm d nhnht nm pha sau hnh tam gic :

Cu hnh R-S v Fischer khng c tng quan trc tip.

a

b

c d

R

a

c

b d

S


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Trong cc hp cht loi andehit glyxeric c s trng hp cu hnh D -andehit glyxeric l (R)-andehit glyxeric, cn L - andehit glyxeric l (S)-andehit

glyxeric.

(D)

C

H

OH

HOH2C CHO

CHOOH

CH2OH

(R)

C

H

OH

HOH2C CHO

OHOHC

CH2OH

(S)

2.3.4.5. Cu hnh cu dng: (a, e) chc ngha i vi xiclohexan m thi.

CHO

OH

CH2OH

H

CHO

H

CH2OH

HO

(L)


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CHNG 3: LIN KT TRONG HO HU C

Nu trong ho v cta hay gp lin kt ion (cn gi l lin kt in ho tr)th trong ho hu c, lin kt cng ho trl lin kt bao trm v quan trng hnc, sau l lin kt phi tr v lin kt hidro xut hin trong mt strng hp.3.1. Lin kt cng ho tr3.1.1. Theo thuyt cin

Thuyt lin kt cin cho rng, khi hai nguyn tkt hp vi nhau, minguyn t gp chung vo mt electron ho tr ca mnh. Cc electron ny chytrn cng mt quo vi cc electron cto nn lp vkh trmi nguyn t.V d:

C

H

H

H

H

Quan nim hin i thng nht vi quan nim cin l khi to nn lin kt

cng ho tr, 2 nguyn tgp chung in t, nhng khc vcch gp chung: do sxen phca 2 obitan.3.1.2. Quan nim hin i3.1.2.1. Obitan nguyn t

Theo chc lng t, cc ht cbn nhelectron, prtn c bn cht nhnguyn: va c tnh cht ht, va c tnh cht sng.

Sroding thit lp phung trnh tng qut vquan hgia nng lngca electron v hm sng xc nh trng thi ca electron trong nguyn t:

H = E (H l ton tHaminton)Khi phng trnh thomn mt siu kin nht nh th hm ssng

l nghim ca phng trnh v c gi l hm sng obitan nguyn tgi tt lobitan nguyn t. Theo nhng kt qu tnh ton, cc obitan ca cc electron ccmc c hnh dng rt khc nhau: obitan s lun lun c dng i xng cu. Ccobitan p c dng hnh s8 ni. Cc obitan p khc nhau vhng:

y

x

z

x

y

x

y

x

z

S P


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Slai ho

Nguyn t cacbon t do trng thi c bn c cu hnh electron 1s

2

,2s22px12py

1. gii thch ho tr4 ca cacbon ngi ta cho rng c mt electron2s chuyn sang obitan 2p cn trng, khi y nguyn t cacbon c cu hnh1s22s12px

12py12pz

1.Khi to lin kt, obitan 2s v mt sobitan 2p c ththp li to thnh

cc obtian c dng khc, dng s8 lch ni, c khnng xen phcao hn, gi lcc obitan lai ho. Kt qutnh ton cho thy, nu coi sxen phca obitan 2s l1, 2p l 3 th cc obitan lai ho sp l xp x2:

1

obitan 2s

1,73 2

obitan lai hoa spobitan 2p Tutheo khuynh hng to ra cc lin kt phn tno hay khng no m

c slai ho sp (2s + 2px), sp2(2s + 2px+ 2py) v sp

3(2s + 2px+ 2py+ 2pz).

Sphn bca cc obitan (m my) lai ho trn khc nhau. Hai m mylai ho sp phn btrn cng mt trc, 3 m my lai ho sp2hng ra 3 nh catam gic u, cn 4 m my lai ho sp3hng ra 4 nh ca tdin u:

1800

1200109028

sp sp2 sp3

3.1.2.2. Obitan phn tlin ktTheo phng php sho trcng nhtheo phung php MO, lin kt

cng ho trc hnh thnh do s xen ph cc obtian nguyn t thnh obitanphn tlin kt. Khuynh hng ca sxen phl tin ti cc i theo nguyn lxen phcc i.Lin kt

Trong s xen ph theo trc, obitan phn t lin kt c trc i xng lung thng ni hai ht nhn, gi l obitan . c im chung ca obitan l ctnh i xng i vi trc lin kt v cc tiu phn (nguyn t, nhm nguyn t)


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c thquay tng i tdo quanh trc m nng lung tng tc khng thay i.trong ho hu c, ta hay gp 2 kiu xen phto lin kt sau y:

sp - s sp - sp *c im ca lin kt :- C si xng theo trc lin kt.- Nng lng lin kt tng i ln (~83 kcal/mol) nn lin kt ny kh bnvng.- Cc nguyn thay cc nhm nguyn thai u lin kt c khnng quay tdo xung quanh trc lin kt m khng lm mt sxen ph(th dH-H, H3C-CH3), do xut hin vn cu dng hp cht hu c.

Lin kt Khi cc obitan xen phvi nhau vc2 pha m trc obitan vn song song

vi nhau gi l sxen phbn ta c obitan phn t, lin kt c to thnhl lin kt . Sxen phnhvy khng su nn km bn. Hai trc ca 2 obitansong song, nm trong mt phng :

Tuy nhin cc tiu phn khng thtquay quanh trc lin kt v nu quayl ph vxen ph, ph vlin kt.

*c im ca lin kt :- Khng c tnh i xng trc.- Cc trc obitan p song song nhau to thnh mt phng gi l mt phng .- Nng lng lin kt tng i nh(~60 kcal/mol) nn km bn hn lin kt ,

n dbphn cc ha hn lin kt .- Cc nguyn thay cc nhm nguyn thai u lin kt khng c khnngquay tdo nhi vi lin kt v khi quay nhthsvi phm sxen phcci ca hai AO, ph vlin kt; do c khnng xut hin ng phn hnh hc cc hp cht c ni i C=C, ni ba CN. . .3.1.3. c im ca lin kt cng ho tr- Bn v rt bn (kim cng).- Cc lin kt cng ho trc di xc nh. di lin kt ca cacbon vi ccnguyn tmt phn nhm tng khi sthttng, vi cc nguyn tca mt chuk th gim khi sthttng, sau na l khi ghp tng th di lin kt gim.


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- Hng khng gian ca cc lin kt l xc nh v lin kt cng ho trc tnhbo ho.

- Hp cht c lin kt cng ho trthng to mng tinh thphn t.- phn cc ca lin kt nh, thng < 1,6D.- Tan t hoc khng tan trong nc, dung dch dn in km.3.1.4. Cc lin kt n, i, ba, hlin hp3.1.4.1. Lin kt n

Trong cc phn tmetan v etan chc lin kt n, l cc lin kt kiu sp - s v sp - sp. Nguyn tcacbon trng thi lai ho sp3. Cc lin kt trong phn tmetan v etan c m tnhsau:

metan etan 3.1.4.2. Lin kt i

Trong phn tetilen, lin kt i C=C gm mt lin kt kiu sp - sp vmt lin kt . Hai nguyn tcacbon trng thi lai ho sp2. Cc obitan xen phto nn nm lin kt . Trc ca nm lin kt ny cng nm trn mt mt phng . Cn li hai obitan p chng sxen phvi nhau to thnh lin kt . Trc cahai obitan ny song song vi nhau, cng nm trong mt mt phng giao nhau trc lin kt C - C v vung gc vi nhau.

C C

H

H

H

H

3.1.4.3. Lin kt ba

Lin kt ba trong phn taxetilen gm c mt lin kt v hai lin kt .Hai nguyn tcacbon trng thi lai ho sp. Cc obitan lai ho sp xen phto nnba lin kt , c trc nm trn mt ng thng. Cn hai obitan pyv pzxen phvi nhau to hai lin kt c mt phng bdc vung gc vi nhau v ct nhau trc lin kt C-C:


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C C HH

3.1.4.4. Hlin hpHlin hp l hc nhiu ni i xen ku n vi ni i nhbuta-1,3-

dien hay vng benzen. Tng tnhetilen, cc nguyn tcacbon trong cc hu trng thi lai ho sp2v hcc lin kt l mt hphng. Cc obitan p xenphvi nhau tng i mt to ra hai lin kt nhtrong buta-1,3-dien hoc xen

phvchai pha to obitan phn tcc lin kt vng kn nhtrong benzen:

H

H

HH

H

H

buta-1,3-dien

benzen Tnh thm, phn thmTnh thm

- Hp cht thm l nhng hp cht vng cha no m tt cnhng nguynt mt vng u tham gia to thnh mt h lin hp thng nht, trong ccelectron ca hto nn mt vng electron kn. Nhng hp cht thm c nhngc tnh m ngi ta gi l tnh thm.

- Cc iu kin ca tnh thm:


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+ Hlin hp hoc p nm trong hp cht vng kn vi selectron l4n+2 (bn trng thi cbn): gi l quy tc thm 4n+2 do Hucken tm ra tnm

1932. Theo quy tc ny th cc polyen vng vi 4n+2 electron phi bn vng vc tnh thm.+ Cc lin kt phi nm trn cng mt mt phng (vng thm phi c cu trc

phng). Vng khng nht thit phi ging benzen m c thl vng cacboxylickhc benzen, dvng hoc vng v cthun tu.+ Nng lng ca hp cht thm thp hn nng lng ca hp cht c cng lin

hp mch h.V d: Hp cht c tnh thm l:

N

benzen piridin naphtalen Hp cht khng thm l:

O

O

N

N

H

H

H

H Tnh phn thm

L nhng hp cht c y 2 yu t(1), (2) nhng c nng lng tn tihoc l bng hoc l ln hn nng lng hp cht mch hc cng lin hp.V d:

xiclo butadien pentalen 3.2. Lin kt phi tr

Lin kt cng ha trphi tr (cn c bit n nhl lin kt cng ha trcho nhn) l mt dng c bit ca kt c to thnh, bn ca n khng khcg so vi lin kt cng ha tr.

Cc lin kt cng ha trphi hp c to thnh khi mt bazLewis (chtcung cp in t) cung cp mt cp in tcho axit Lewis (cht nhn in t) vhp cht to thnh sau c gi l adduct.

Cc lin kt phi tr c th tm thy trong nhiu cht khc nhau, chng hnnh trong cc phn tn gin nhmonoxit cacbon (CO), trong c mt linkt phi tr v hai lin kt cng ha tr thng thng gia nguyn t cacbon v


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nguyn t oxi, hay trong ion amoni (NH4+), trong lin kt phi tr c to

thnh gia proton (ion H+) v nguyn tnit.

Cc lin kt phi tr cng c to ra trong cc hp cht thiu in t, chnghn nh trong clorua berili rn (BeCl2), trong mi nguyn tberili c linkt ti bn nguyn tclo, hai vi lin kt cng ha trthng thng v hai vi linkt phi tr, iu ny sto cho n mt cp tm (octet) n nh ca cc electron.

Cc lin kt phi tr cng c thtm thy trong cc phc cht phi tr c stham gia ca cc ion kim loi, c bit nu chng l cc ion kim loi chuyn tip.Trong cc phc cht ny, cc cht trong dung dch hot ng nhcc bazLewisv cung cp cc cp electron tdo ca chng cho ion kim loi, trong lt n hotng nhcc axit Lewis v nhn cc electron. Cc lin kt phi tr to ra cc hpcht gi l phc cht phi tr, trong khi cht cung cp electron c gi l cc

phi t.C rt nhiu cht vi cc nguyn tc cc cp electron c c, chng hnoxi, lu hunh, nitv cc halogen hay cc ion halogenua, m trong dung dch cthcung cp cc cp electron trthnh cc phi t. Mt phi tthng thngl nc (H2O), n sto thnh cc phc cht phi tr vi bt kion kim loi ngmnc no. Chng hn Cu2+, to ra [Cu(H2O)6]

2+trong dung dch nc. Cc phit n gin khc l amoniac (NH3), cc ion florua (F

-), clorua (Cl-) v xianua(CN).

Lin kt phi tr l mt loi lin kt cng ho trm ccp electron lin kt

do mt nguyn tcung cp, nh lin kt N-O hoc S-O trong triankylamin oxitcng nhtrong diankyl sunfoxit:

N

R

OR

R

S

R

R

O

Lin kt phi tr cng c thhnh thnh gia hai phn tnh:

H3N: + B(CH3)3 H3NB(CH3)3

3.3. Cc loi lin kt yu3.3.1. Lin kt hydro3.3.1.1. Bn cht ca lin kt hydro

Lin kt hydro l lin kt hnh thnh gia hai nguyn t c tnh m inqua nguyn thidro. y, nguyn thidro ng vai tr cu ni. Lin kt hydroc bn cht tnh in v theo mt sdkin mi, ngi ta thy n c phn do tophc cho nhn, v d: H-F...H-F.

Lin kt hydro l lin kt yu, chvo khong 5kcal/molMun c lin kt hydro X-H...Y, X v Y phi l cc nguyn tc m

in ln v kch thc nh, X c lin kt cng ho trvi H v Y phi c i in


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tcha lin kt. Ni cch khc, X-H l axit yu v Y l bazyu, v nu khngnhvy sto ra lin kt phi tr hoc khng lin kt.

Lin kt hydro c th hnh thnh l lin kt lin phn t (A) v lin kthydro ni phn t(B) (Ch n iu kin khng gian: Phn tphi c cu hnhnhthno cho tng tc ni phn t(to ra lin kt hydro) dn n shnhthnh nhng vng nm, su cnh vi hiu ng nng lng cao nht. Chnh v vy,hu nhchc ng phn octo mi c lin kt hydro ni phn t. Cc - glycol,- aminancol, - xetancolc lin kt hydro nphn tnhng tng i kmbn. Nu trong mt cht c lin kt hydro ni phn tyu (v dtrong o clo phenol ) th khi ho tan cht vo dung mi c khnng nhng e-cao (axeton,ioxan) th lin kt hydro bt ra v xut hin lin kt hydro mi gia cht tan vdung mi):

...O - H...O - H...O - H...O

R R R

A

O

C H

O

HO

B Vi cc iu kin , X v Y thng l O, N, F.Quy lut: Lin kt hydro tng t tri qua phi theo chu k v tng tdi

ln trn theo nhm.3.3.1.2. Tnh cht ca cc hp cht c khnng to nn lin kt hydroLin kt hydro nh hng ng kn tnh cht ca hp cht.

- Nhit si v nhit nng chy ca hp cht c lin kt hydro lin phn ttng nhiu nhso snh nhit si ca ru metylic CH3OH v ru thiometylicCH3SH l 66

0C v 60C v cc phn ttrong cht brng buc vi nhau thnhnhng phn t ln hn. Nc, ancol, phenol, amoniac, amin bc mt, amin bchai, axit cacboxylicl nhng cht chu schi phi ca quy lut ny. Cn lu ltrong khi lin kt hydro gia cc phn tlm tng nhit si v nhit nngchy ca cht th lin kt hydro ni phn tli khng gy c nh hng nhvy. V d cc dn xut hai ln th ca benzen, nu hai nhm th trong vngkhng c khnng lin kt hydro vi nhau th hai ng phn ct v para ni chungc nhit si gn nhnhau nhng nu hai nhm th lin kt hydro vi nhauc th ng phn octo (lin kt hydro ni phn t) lun si nhit thp

hn nhiu so vi ng phn para (c lin kt hydro lin phn t).- tan ca cc cht c khnng to lin kt hydro vi dung mi tng ln nhancol etylic tan v hc trong nc cn etan tan rt t (4,7%). V vy cc ru,amin, axit thp cng nh cc cht c phn t lng khng nh nh glucoz,sacaroz, polyvinylancol, u tan tt trong nc. Tinh bt v protit tuy c phntlng rt cao nhng nhc lin kt hydro nn c th to ra nhng dung dch


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keo. Cc ancol, amin, axit cacboxylic tan trong nc c thng vai tr cht chohay nhn prton khi to thnh lin kt hydro. Nhng hp cht khc nhandehyt,

xton, ete, este khi y chc thl cht nhn prton m thi. tan ca cc chttrong nc cn ph thuc vo kch thc ca gc hydrocacon lin kt vi ccnhm chc. Gc cng ln th tan cng gim. ng ch l tan ca cchp cht thm c hai nhm thv c khnng lien kt hydro, trong khi cc ngphn meta v para thng d tan so vi ng phn octo trong cc dung mi mchng c th to ra lin kt hydro lin phn tnh nc, ru. Cc ng phnocto vi lin kt hydro ni phn tli dtan tong cc dung mi khng phn ccnhiu hn.- Lin kt hydro cn nh hng ti bn cc ng phn (sc mt ca lin kthydro ni phn tnht l khi lin kt hydro tham gia vo mt hlin hp vng(c nng lng lin kt cao hn) c th lm cho mt ng phn ca cht hu ctrnn bn vng hn) v tnh cht axit, bazca phn t.3.3.1.3. ngha ca lin kt hydro- Dng gii thch tnh cht bt thngvvt l v ho hc ca hp cht.- L nn tng cbn ca ssng (lin kt peptit).- C ngha quan trng trong cc cng tnh xy dng.- Lin kt khng bn nhng quan trng.

3.3.2. Lin kt Vandecvan3.3.2.1. Khi nim: L lin kt c hnh thnh gia cc phn tvi nhau bng c cc ca chng. Lin kt ny c tc dng gicc phn tcng ho tr li vinhau tp hp chng trong mt trng thi no ca vt cht: Lng, rn, kh.

- Lin kt Vandecvan (V) c bn cht tnh in, lin kt V khng c bn cht hohc m c bn cht vt l.- Lin kt V yu hn lin kt hydro (ELK= 2 10kJ/mol). E lin kt nm trongkhong l do tuthuc vo shnh thnh ca cc nguyn t.- Bn knh V (rV) l 1/2 khong cch gia hai nhn ca hai nguyn t thuc haiphn ttham gia lin kt.- Nhc lin kt V m con ngi gii thch c mt shin tng nhma,...3.3.2.2. Nng lng ca lin kt Vandecvan3.3.2.2.1. Bn cht ca lc V

Ngun gc ca lin kt V cha c gii thch hon ton y tuy nhin

theo V th lin kt V c bn cht tnh in bao gm lc ht v lc y.3.3.2.2.1.1. Lc ht: Khi khong cch gia cc phn tt n gi trcn bng thto ra lin kt V c ngha l xut hin lc ht. Tuy nhin trong tng trng hp thlc ht c nhng bn cht khc nhau. Lc ht bao gm:Lc nh hng

i vi nhng phn tc cc ( 0), gia cc phn tlng cc, c lctng tc tnh in Coulomb. Ngoi lc ht, gia cc lng cc cn c cc lcy tng h. Tuy nhin, v phn t c khuynh hng nh hng sao cho hthng l thun li nht vmt nng lng ng vi mt trng thi vng bn nht,ngha l c khuynh hng nh hng ngc chiu nhau nn lc ht gia cc phn


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52

t lng cc s chim u th. Do vy, hiu ng trn c gi l hiu ng nhhng.

Hiu ng nh hng cng ln khi momen lng cc ca phn tcng ln.Ngc li, hiu ng nh hng gim khi nhit tng v chuyn ng nhit cntrsnh hng tng hca cc phn t. Ngoi ra lc ht ln nhau gia ccphn tc cc sgim nhanh khi khong cch gia chng tng.Hthc nng lng:

Uh =kTr6

4

3

2

Trong :Uh: Nng lng tng tc ca hai phn tc momen lng cc l .R: Khong cch gia hai phn t.

T: Nhit tuyt i.k: Hng sBoltzmanLc cm ng

Nhng phn tkhng c cc cng bphn cc ho di tc dng ca intrng ca cc phn tc cc hay ca cc ion ln cn, sphn cc ny gi l sphn cc ho cm ng v tng tc gia cc phn tdo hin tng phn cc hocm ng trn gi l hiu ng cm ng.

Hiu ng cm ng cng mnh nu hsphn cc ho v momen lngcc ca phn tcng ln. Ngc li, hiu ng cm ng gim nhanh khi khongcch gia cc phn ttng. Hiu ng nh hng khng phthuc vo nhit .

Hiu ng cm ng c bai nghin cu, theo ng, nng lng tng tccm ng tc l nng lng tng tc gia mt lng cc vnh cu v mt lngcc cm ng xut hin trong phn tln cn c tnh theo hthc:

Uc = - 622

r

Lc khuch tnVi hai hiu ng trn, ngi ta vn cha gii thch c lc ht tng h

gia cc phn t, nguyn tkhng c mmen lng cc vnh cu, c bit l giacc kh tr.

Tng tc V cn c gii thch bng hiu ng ny trn csca chc

lng tc London xy dng nm 1930.Theo thuyt ny, v cc ht cu to nn phn t, nguyn tlun trng thichuyn ng lin tc nn trong qu trnh chuyn ng ny, sphn bin tchtrnn bt i xng, do lm xut hin nhng lng cc tc thi v stngtc gia cc lng cc ny l nguyn nhn thba ca tng tc V. Hiu ng nygi l hiu ng khuch tn.

Hiu ng khuch tn c gii thch bng sphn cc ng ca phn thay nguyn t. Nng lng ny c xc nh mt cch gn ng theo hthc:

Ukt= - 62

0

4

3

r

h


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Trong :

0 : Tn sdao ng ng vi nng lng im khng, E0 =

2

0h .

Nng lng khuch tn tlnghch vi r6v khng phthuc vo nhit .Hiu ng khuch tn tn ti mi h in t ngha l mi phn t,

nguyn tc cc hay khng c cc.Tm li: trong trng hp chung i vi nhng phn tc momen lng cc vnhcu v hsphn cc ho , nng lng tng tc (ht) V c xc nh theohthc:

Uh= -

++

4

32

3

21 02

24

6

h

kTr

3.3.2.2.1.2. Lc y: Xut hin khi khong cch gia cc phn t< khong cch

cn bng r0Nng lng y tnh theo hthc:

U = b.e-cr trong b, c l nhng hng s

Nh vy nng lng tng tc ton phn gia cc phn tc tnh theo hthc:

U = Uh + Ud3.3.2.2. Quy lut- M phn tcng tng th lc V tng.- Cu trc phn tcng phng th lc V cng tng.- Tt ccc lc ht tng th lc V tng.

- Quy lut khong cch tc dng: Bn knh tc dng ca lc V mr61 . ph v

lin kt V th phi lm cho khng cch tc dng gia cc phn t>6

1

rm.

3.4. Mt sloi lin kt khng mang bn cht ho hc3.4.1. Lin kt bc Clatrat

- L lin kt to thnh do slng chp nhng phn tloi ny vo khong khnggian ca nhng phn tloi khc m khng to ra lin kt ho hc bnh thng.Nhvy, trong hp cht bc phi c hai thnh phn chnh:

+ Phn tlm lng cha c gi l phn tch.

+ Phn tnm trong lng c gi l phn tkhch.- Lc tc dng trong hp cht bc l nhng lc lin kt yu, trong c thc lcV, tng tc lng cc nh hng, sbao bc n gin, v.v....Mt khc nhnglc cn phthuc tng loi thnh phn ca hp cht bc.V d: Hp cht bc ca ur

+ Ur l phn tch.+ Hidrocacbon l phn tkhch.


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3.4.2. Lin kt Catnan, RtaxanTrong ho hu cthng gp nhiu hp cht a vng ngng thay ri rc,

trong phn t ca nhng hp cht ny, cc vng lin kt vi nhau bng lin ktho hc vi stham gia ca mt se-ho tr.Ngi ta tm ra cc hp cht a vng kiu khc gi l catnan, trong

cc vng lun vo nhau nhnhng vng xch:

Nhvy, lin kt gia hai vng y khng phi l lin kt ho hc m ctnh cch chc.

iu ch catnan gm nhng vng cha t nht l 20 nguyn t cacbon.Hiu sut iu chthp.

Rtaxan c cu to theo cch gn tng t catnan: mt vng ln vyquanh mt mch di ni vi hai nhm i phn thai u


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CHNG 4: HIU NG CU TRC PHN T4.1. Hiu ng in t

4.1.1. Khi nim4.1.2. Phn loi: 3 loiHiu ng cm ngHiu ng lin hpHiu ng siu lin hp

4.1.2.1. Hiu ng cm ng (k hiu l I:Ting Anh Inductive Effect)a. Khi nim

Hiu ng cm ng l sphn cc lan truyn cc lin kt lin tip theo mchlin kt do s phn cc ca mt lin kt no (hoc do s ht hoc yelectron ca mt nguyn thay nhm nguyn tno trong phn t).

V d: Trong n propyl clorua, do m in ca Cl m lin kt C-Cl phncc ko theo sphn cc ca cc lin kt C1 C2, C2 C3

CCl C C H

H

HHH

HH b. Cch biu din: Dng mi tn chchiu in tchuyn dch.c. Phn loi

Ty theo tnh cht ca nhm gy hiu ng, ngi ta phn loi hiu ng cmng thnh hiu ng cm ng m (-I) v dng (+I).

Hiu ng cm ng m gy ra bi nguyn t hay nhm nguyn t htelectron vpha mnh, nh Cl, Br, NO2(X).

Hiu ng cm ng dng gy ra bi nguyn thay nhm nguyn tyelectron ra khi n nh CH3, C2H5, O

-, (X).Ngi ta cn thy c hiu ng trng (F) l hiu ng cm ng truyn lc

tnh in qua khong khng gian gia cc nguyn tgn nhau khng lin kt vinhau.

Qui c: Hiu ng gia cacbon v hidro = 0 (IC-H= 0).d.c im

Hiu ng cm ng gim nhanh theo chiu di mch truyn.+>+>+ 321

Hiu ng cm ng khng bcn trbi yu tkhng gian.e. Quy lutCc gc hidrocacbon no c hiu ng +I, hiu ng cng mnh khi bc ca gccng tng, cc gc hidrocacbon khng bo c hiu ng I, gc cng khng no thhiu ng I cng ln.

+I: CH3 - < CH3CH2 -


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- F > - Cl > - Br > - I- OR > - SR > -SeR

- F > - OR > - NH2Cc nhm mang in dng c hiu ng I, cc nhm mang in m c hiung +I. in tch cng ln hiu ng cng mnh.

+I: - O-< - S-< -Se--I: - O+R2> - S

+R2> -Se+R2 ; - N

+R3> - NR2V dvbiu hin cc quy lut trn l tnh cht axit ca cc axit th. Cc

nhm c I cng mnh v cng gn nhm COOH th tnh axit cng mnh.f. ngha

- Dng gii thch tnh cht bt thng hoc tnh cht ca cc hp cht hucnhtnh axit,

- Dng gii thch hng phn ng v cchxy ra ca phn ng.4.1.2.2. Hiu ng lin hp (k hiu l C:Ting Anh ConjugationEffect)a. Khi nim

- Hlin hp l cc hcc lin kt i xen kcc lin kt n. Cc electronp c xem nhlin kt i.V d:CH2= CH CH = CH2 ( )CH2= CH CH = CH CH = O ( )CH2= CH CH = CH OH ( p )

Trong hlin hp, obitan phn tbao trm tt ccc nguyn tch, tagi l obitan gii to.

- Hiu ng lin hp: Hiu ng lin hp l s phn cc lan truyn ccelectron trong h lin hp khi c sdch chuyn cc electron hay p no ca h.V d:

CH2 CH CH CH CH O Do sdch chuyn electron ca nhm CH=O. Ngi ta phn bit hiu ng linhp tnh (Cs) do cu trc ni phn tm lun lun c, nhtrng hp trn vhiu ng lin hp ng (C) chxut hin khi c tc ng bn ngoi, chng hn,phn tbutaien i xng khi c HBr th bbin dng v xut hin hiu ng (theo

chiu mi tn cong)CH2 CH CH CH2 H+Br- Tuy nhin, v Csv C cng mt c tnh nn ngi ta chdng khi nim chung:Hiu ng lin hp C.b. Cch biu din: Dng biu din chiu chuyn dch ca in t.c. Phn loi v quy lutHiu ng +C (hlin hp y in tra khi n?): Cc nhm X gy hiu nglin hp dng +C ni chung u c cp electron d trong h p- , tham giachuyn electron vpha lin kt :

..


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X C C

Cc nhm ny thng c c-I.Quy lut+ Hiu ng +C ca cc nguyn t cc nguyn tgim khi s th t tng

trong mt chu k hoc mt phn nhm:NR2> OR > FF > Cl > Br > I

+ Nguyn tmang in tch m c hiu ng +C ln hn chnh nguyn ty: O-> OR.Hiu ng -C (hlin hp ko in tvpha mnh): a scc nhm cha nou gy hiu ng lin hp m -C ht in tvpha mnh nhNO2, CN, CHO,

COOH. Cc nhm ny ng thi c chiu ng -I:C C C Z

Quy lut: Hiu ng -C ca nhm C = Z cng tng nu:+ Z cng bn phi trong mt chu k.+ Z mang in tch dng.+ Z tham gia lin kt bi tng

- C = O > - C = CR2- C = N+R2> - C = NR- NO2> - C N > - C = O > - COOR > - COO

-Mt snhm c lin kt bi C = C sc hiu ng +C hay -C l tuthuc vonhm lin kt vi chng nh:

CH2 C Cl

+C-C

CH2 CH CH O

-C+C d.c im- Hiu ng lin hp chthay i t khi ko di mch lin hp.- Hiu ng lin hp chxut hin trn hlin hp phng tc l hobitan gii to.- Hiu ng lin hp chu nh hng ca hiu ng khng gian.e. ngha: Ging hiu ng cm ng.

4.1.2.3. Hiu ng siu lin hpH: HyperconjugationEffect (phbin l hiung lin hp )a. Khi nim

Hiu ng siu lin hp l hiu ng electron do tng tc gia cc electronca lin kt C - H hay C - F vi electron ca ni i hoc ba cch nhau mtlin kt n C - C:

C

H

H

H

CH CH2


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Ngi ta gii thch rng cc lin kt C - H tp hp li thnh obitan nhm,nhmt ni ba, ni i gi. Hiu ng siu lin hp yu v pht huy tc dng

trng thi phn ng mnh hn.b. Phn loi v quy lutC hai loi hiu ng siu lin hp:

Hiu ng siu lin hp dng (+H) ca cc lin kt C - H y in tvphani i, theo chiu ca hiu ng +I, nhng c quy lut ngc nhau:+I: - CH3< CH3CH2- < (CH3)2CH - < (CH3)3C -+H: - CH3> CH3CH2- > (CH3)2CH - > (CH3)3C -

Hiu ng ny do Baker v Nathan pht hin nm 1935 khi nghin cu phnng: p-R-C6H4CH2Br + piridin nn gi l hiu ng Baker Nathan.V d:

CH2Br

CH CH3

CH3

CH2Br

C CH3

CH3

CH3

CH2Br

CH3

CH2Br

CH2CH3

Hiu ng siu lin hp m (-H) ca cc lin kt C - F ht in tca lin kti:

C

F

F

F

CH CH2

Ngi ta chng minh c hiu ng -H ca nhm CF3khc vi hiu ng -I

ca n.c. ngha- Gii thch c tnh linh ng ca nguyn tH khi lin kt C-H gn trc tip vinguyn tC mang lin kt bi hoc nhn thm:

- Gii thch c tnh bn ca but-2-en hn hn but-1-en do hiu ng siu lin hpc mrng hn:

C C

O

H

H

H

H


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4.2. Hiu ng khng gian S (Ting Anh Steric Effect)4.2.1. Khi nim:Hiu ng do kch thc ca cc nhm nguyn tgy nn cgi l hiu ng khng gian (S).

V d1: Trong phn t2.6-imetyl quinon di y c hai nhm C=O song chcC=O tham gia phn ng vi NH2OH, cn C=O khng phn ng c v hai nhm

bn cnh gy hiu ng khng gian cn trNH2OH n gn:CH3

CH3

OO(1) (2)

V d2: Phenol l mt axit yu, nu a nhm NO2vo vtr para slm tngmnh tnh axit v nhm ny gy hiu ng - C v - I. Tuy nhin, nu cc v tr

ortho i vi nhm NO2 c nhng nhm CH3 th tnh axit ch tng t v hainhm CH3 gy hiu khng gian, lm gim slin hp do gim hiu ng -C ca NO2.

4.2.2. Phn loi:Hiu ng S rt a dng, song phbin hn cl:Hiu ng khng gian loi mt (S1)Hiu ng khng gian loi hai (S2)Ngoi ra cn c hiu ng oct l hiu ng ca nhng nhm thvtr oct ivi nhau. Khng nn coi hiu ng oct l hiu ng khng gian n thun m lmt hiu ng hn hp trong thng c yu tkhng gian.

4.2.3. Hiu ng khng gian loi mt (S1)Hiu ng khng gian loi mt (S1) l hiu ng ca nhng nhm thc kchthc tng i ln chim nhng khong khng gian ng kv do cn trhayhn chkhng cho mt nhm chc no ca phn ttng tc vi phn thayion khc, hoc lm thay i hiu snng lng tdo F gia phn tv trng thichuyn tip.V d: Phn t 2,6-imetyl-1,4-quinon c hai nhm cacbonyl nhng ch c mtnhm trong tham gia phn ng vi NH2OH (hidroxylamin) cn nhm thhai vbn ngkhng gian bi hai nhm metyl nn khng li gn phn tNH2OH phn ng c.

C C

H

H

H CH C

H

H

H

but-2-en

CH3 C

H

H

CH CH2

but-1-en


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O

O

CH3H3C

Cn lu rng trong mt phn ng lng phn tnh hng khng gian c

thdo cht phn ng hay do tc nhn hoc do chai cng gy nn. L tt nhintrong trng hp sau cng (chai cng gy nn) nh hng t ti mc cao nht.

Khi xt kh nng phn ng th u tin u tin xt tiu ch in ttrc ri mi xt nh hng ca khng gian

4.2.4. Hiu ng khng gian loi hai (S2)L hiu ng ca nhng nhm thc kch thc ln vi phm tnh song

song ca trc cc m my electron v n trong hlin hp (gy ra bin i vmt cu trc ca cc h lin hp). Loi hiu ng ny thng gp cc hp chtthm.

V d: N imetylanilin dtham gia phn ng ghp i vi mui iazoni vtrpara do hiu ng +C ca nhm N(CH3)2. Trong khi dn xut 2,6-imetyl caamin ny li khng tham gia phn ng do hiu ng khng gian lm cho nhmN(CH3)2bxoay i, do sxen phgia cc obitan v n bvi phm v hiung +C gim.

N

H3C

H3CC6H5N2

+

N

H3C

H3C

N N

CH3CH3

N

CH3H3C

Hiu ng khng gian loi hai thhin rt r qua cc tnh cht vt l nh

momen in, quang ph,v.v... cho nn c thdng rng ti cc phng php vt lkho st loi hiu ng ny.


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4.2.5. Hiu ng octTa bit rng cc nhm th v tr octo trong vng benzen thng gy

nhng nh hng rt bt ng (khc nh hng ca nhng nhm cc v trkhc) n tnh cht vt l cng nhtnh cht ho hc ca phn t.Th d: Khi sosnh hng sphn ly Kaca cc axit C6H4(R)COOH, ta thy hu nhbt kbncht ca nhm thl g ,cc axit ng phn oct lun lun c Kaln hn cc ngphn khc. Loi nh hng c bit ca cc nhm thvtr oct nhvy gi lhiu ng oct.

Vi danh t hiu ng oct ta hiu l loi hiu ng hn hp bao gmnhiu yu t, m nhng y t c khi li c tc dng nghch hng vinhau.Cc yu t l :

a) Hiu ng khng gian loi mt: Nhm thX vtr octo cn trs tncng ca tc nhn Y vo nhm chc Z:

X

Z

Y

b)Hiu ng khng gian loi hai:Nhm thX lm mt tnh phng ca h:

X

Z c) Hiu ng cm ng:v tr octo hiu ng cm ng thhin mnh hn

nhiu so vi cc v tr khc v khng nhng nhm gn nhm chc hn,mcn c thtc dng trc tip nhhiu ng trng:X

Z

F

d) Tng tc hyr: to thnh lin kt hyr ni phn t:

C

O

HO

O

H

C

O

O

H

O

H

Trong tng trng hp cth, c thkhng phi tt cm chmt vi yu

tktrn cng xut hin thi.


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CHNG 5: TNH AXIT-BAZCA HP CHT HU C5.1. Khi nim axit - baz

5.1.1. Thuyt axit, baz5.1.1.1. Thuyt ArheniusAxit l nhng hp cht c cha Hydro, khi phn ly trong nc cho ion H+.

HnX nH++ Xn-

HCl H+ + Cl-Baz l nhng hp cht c cha ion OH-, khi phn ly trong nc cho ion

OH-M(OH)m M

m+ + mHO-Ca(OH)2 Ca

2+ + 2HO-* u im

- Phn loi c thnh cc hp cht axit, baz.- Gii thch c bn cht ca phn ng trung ho: H+ + HO- H2O- Gii thch khnng xc tc: tnh xc tc tng khi [H+] tng.- Thao tc n gin, dvit.* Nhc im- Khng gii thch c tnh axit, bazca mt shp cht nhNH3, AlCl3, xphng.- Khng gii thch c cho nhng hp cht lc ny l axit nhng lc khc n lbaz.5.1.1.2. Thuyt Liwis

Axit l nhng cht trong c thl ion, nguyn thay phn tc khnng kt hp vi i in ttdo ca baz.

Cc axit theo Lewis c:- Proton

H++ :NH3 NH4+

H++ CH2=CH2 CH3-+CH2

- Cc cationLi++ CH3OH CH - O

+Li - HAg++ 2NH3[H3N:Ag:NH3]

Tnh axit ca cc cation tngkhi:+ in tch dng ca cation tng: Fe+2< Fe+3

+ in tch ht nhn ca cation tng: Li+< Be+2< B+3+ Bn knh ion gim: K+< Na+


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+ in tch ca ht nhn nguyn ttrung tm tng (p dng cho cc nguyntcng nhm).

+ m in ca cc nguyn tlin kt vi nguyn ttrung tm tng.+ Bn knh nguyn ttrung tm gim.+ Slp in txung quanh nguyn ttrung tm gim.

- Cc nguyn t c 6 in t lp ngoi cng v d nh oxy, lu hunh, ccnguyn tny c thtng tc vi bazto ra lp ngoi cng 8e-.

O NR3 O NR3

- Cc hp cht c ni kp bphn cc

C

O

HR RCH = OCN- C

O-

H

CNR

- Cc hp cht m lp in tngoi cng c

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