- ISOMERISM-.doc

8/16/2019 - ISOMERISM-.doc

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ISOMERISM

The acorance of more than one compounds of same molecular formula is calledisomerism and such compounds are known as isomers.

eg CH3 – O – CH3 and CH3 – CH2 – OH

(C2H6O) O

CH3CH2 – CHO and CH3 – C – CH3

(C3H6O)

ince isomers are different compounds the! ha"e different ph!sical and chemical

properties. tructural tereo # pace

Or constituitional configratinal # conformational

Chain

$ositional ⇒ %eometrical

&ing chain

'unctional

etamers ⇒ Optical

Tantomers

→ tructural "ersus stereo isom. somers differing in connecti"it! of atom are calledstructral isomers.

eg CH3 – CH – CH3 and CH3 – CH2 – CH2 – OHOH

CH3 – O – CH3 and CH3 – CH2 – OH

somers ha"e same connecti"it! of atom *ut different spetial arrangement of atom or

group a*out a centre or *ond are called stereo isomers.

Cl

CH2 – CH2 and CH2 – CH2

CH3 CH3 CH3 H

C + C and C + C etc.H H H CH3

Chain isomers, str. iso. -iffering in chains of C – atom.

eg CH3 – CH2 – CH2 – CH2 – CH3 and CH3 – CH – CH2 – CH3

CH3

Positional isomers: differing in position of an atom # group.


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CH3 – CH – CH3 and CH3 – CH2 – CH2

OH OH

/ctuall! onl! those

tr. will chain isomers in which parants chain are different otherwise positional isomers.

eg () CH3 – CH2 – CH2 – CH2 – CH2 − CH2 – CH3

(2) CH3 – CH2 – CH – CH2 – CH2 – CH3

CH3

(3) CH3 – CH – CH2 – CH2 – CH2 – CH3

CH3

(0) CH3 – CH – CH – CH2 – CH3

CH3 CH3

() s the chain isomer of all (2) is chain isomer of (i) and (i") *ut positional isomer of

(iii).

Ring – chain isomers: f one isomer has ring str. while the other has open chain str. then the!

CH3 – CH + CH2 or1

CH2 + CH – OH or1

CH3 and1 CH – CH2 – CH3

CH3 oth howe"er can ha"e ring *ut then the sie of

rings is should *e different.

Functional : 'unctional group differ.

eg O O

CH3 – C and H – C – OCH3

OH

CH3 CH2 OH CH3 – C – CH3

O

CH3 – CH2 CHO CH3 – C – CH3

*** Metamers : functional group not mono"alant. f no. of C – atom differ either side at

the functional group.

eg CH3 – CH2 – O – CH2 – CH3 and CH3 – O – CH2 – CH2 – CH3

444 Tautomers, → &eadil! inter con"erti*le structural isomers.

2

CH3

OH

CH3

OH

CH3

OH


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O O

CH3 – C and CH3 – CH2 – C

CH3 . H

O OHCH3 – C CH2 + C

CH3 CH3

O .

CH2 – C

H CH3

.

and one not are intercon"erti*le therefore and are tautomers of each other.

→ Tautomers are different compels therefore the! ha"e different ph!sical and chemical properties. 5"en then it is "er! difficult to separate then. This is *ecause tautomers eist

in a state of d!namic e7uilm. Howe"er separation is possi*le speciall! when all tautomersare in good proportions and emplo!ed techni7ue does not allow enter con"ersion.

O OH

CH3 – C CH2 + C

889 CH3 9 CH3

∴ con:t *e separate

f we take1O O OH O

CH3 – C – CH2 – C – CH3 CH3 – C + CH – C – CH3

;9 H – release.. 829

∴ can *e separate.


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O

4 $H – C – H

O

4 $H – C – $HCH3 – CH + >H2 CH2 + CH – >H2

O

CH3 – CH2 – CH2 – C – H

444 $ercentage enol content, → $ercentage enol content depend upon

(a) ta*lit! of enol ? $5C ∝ sta* of enol

(*) /cidit! of enolia*le H ? greater is the acidit! higher will *e 5C.

(c) ol"ent (d) Temparature,

Stability factor: O OH

CH3 – C – CH3 CH2 + C – CH3

C + O C + O

C – H O – H

4 ( 5 C + O @ 5 C – H) A (5C + C1 5 O – H) therefore in this case ketoform is moresta*le than enol form.

O O OH O

CH3 C CH2 C CH3 CH3 C CH C CH3

/cet!l acetone,

ta*iliation energ! C + O C + C 1 OH H – *ond etended resonance.

C – H

n case of acet!l acetone enol form is more sta*le then ketoform.

O O OCH3 C CH3 CH3 C CH2 C CH3

.

∴ enol content A .


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. $H C CH2 C $H C + CH – C – CH3

O O O O

. CH3 O C CH2 C CH3 − C – CH3 A − C – OCH3

O O

B. CH3O – C – CH2 – C – OCH3

enol content ? A A A B.

(2)

. .

enol content A .

(3) CH3 CH3

C + O C + O C + O

H CH3 CH3

.

enol content A A .

(0)

enol content A A

5noliation? enoliation can *e either acid # *one catal!sed

/cid catal!sed process?

O H@ OH OH

CH3 C CH3 CH2 C CH3 CH2 + C – CH3 – H

H

H@ protonates car*o!lic O: and thus clea"age C + O and C – H *ond *ecomes "er!

eas!.

ase catal!sed process.

O OH− O

CH2 C CH3 CH2 – C CH3

↓

O H – OH ↓

CH2 + C – CH3

O

D

OO

O OOH

δ−δ−

δ−

δ−

O O O


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CH2 + C CH3 @ OH

O O O

CH3 C CH2 – CH3 CH3 C CH2 C CH3

H@ OH H@ OH−

OH OH O

OH CH2 + C CH2 – CH3 CH3 – C + CH – C CH3

CH3 – C CH – CH3 .

is more sta*le than . *ecame more su*stituted (+) is more sta*le.

CH3

C + CH2 A CH3 – C + CH2

CH3

n acid catal!sed process sta*ilit! of enol is dri"ing force *ut in *ase catal!sed pro"es

acidit! of enolia*le – H is the dri"ing force.

444 sotope echange

& – OH → O D2 & – O-.

CH3COOH → O D2 CH3COO-.

echanism , − & O HOδ@

& Hδ−

Oδ−

-δ@ – Oδ−

-δ@

&

O @H

- O

-

T.. O#H *ond can *e echange *ut not C – H *ecause in C – H *ond H is not protic.

O O

$H C CH3 → )(2 excessO D $H – C C-3

$ropose mechanism E

O O – H O – -

6

OH-2O

-

O

O

H

-

&

-


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$H C CH3 $H – C + CH2 → O D2 $H – C CH2

O – - O – H O

$H – C CH ← O D2 $H – C CH $H – C CH2

- - -

O O – H

$H – C C-2 $H – C C-2 → O D2

H

O O – -

$H – C C-3 $H – C C-2

⇒ Effect of temperature on enol content:

O O OH O

CH3 C CH2 C CH3 CH3 C CH C CH3

2DoC 9

3DoC ! 9

0DoC 9

A ! A . /t high temperature H – *ond *reaks therefore enol content decreases.

⇒ Solvent effect on enol content:

O O OH O

CH3 C CH2 C CH3 CH3 C CH – C – CH3 %as phase 9

in H2O ! 9 F A !G

n water keto form makes H – *ond with water molecules1 therefore need to go in enol

form decreases.

O OH

CH3 C CH3 CH2 + C CH3

3DoC 9

Do

C ! 9 F A !G⇒ onfigurational verses conformational isomers:

f stereo isomers cannot *e inter con"erted without clea"ing an! *ond then the! are calledconfugrational isomers on the other *and if this intercon"ersion is possi*le without

clea"ing an! *ond then the! are called conformational isomers.

Cl

CH2 – CH2 CH2 – CH2 conform.

I


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r Cl r

CH3 CH3

C + C configraH H

/ *ond has to *e clea"ed

CH3 H

C + C

CH3 H

⇒ !eometrical isomers:

Configrational isomerism arising due to different spetial arrangement of atoms or groups

a*out a *ond along which rotation is restricted is called geometrical isomerism these *onds on *e multiple *ond or single *onds of ring.

"# %eometrical isomers is possi*le along which of the following multiple *onds.

(a) C + C (*) C ≡ C (c) C + > (d) C + O (e) > + >

>ote – that two isomers can *e geometrical isomers onl! if the! differ in spetial distance

*etween the groups.

"# %eometrical isomers occur with , −

(a) /lkene (*) /lk!ne (c) imines (d) ketones (e) h!dragone.

(i) case of C + C *onds, − geometrical isomers a*out C + C *ond will *e possi*le onl! if each C: of the dou*le *onds *ears two different groups.

a l a a

C + C C + C

* m * *

a *

C + C

a *

CH3 – CH + CH – CH2 – CH3 CH3CH2 – CH + CH – CH2 – CH2 – CH3

CH2 + CH – CH + CH2

CH2 + CH – CH + CH – CH3

CH2 – CH + CH – CH + CH – CH3

ase of $ bon% in ring :

;

H

H

•

•

H2

H2


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>o geometrical isomers *ecause trans configuration is not possi*le. Howe"er it *ecomes

possi*le from ; – mem*ered ring onwards.CH3 – CH + C + CH – CH3

CH3 – CH + C + C + CH – CH3 CH3 CH3

C + C + C

H H

umelens

(i) 5"en no. of C + C *ond

→ geometrical isomers isomerism(ii) Odd no. of C + C *ond

→ geometrical isomers occurs if each and *ears two different JJJJJJJJJJJJJJJJJJ.→ Ca*in – ngold – prelog se7uence rule, − () The group ha"ing first atom of high atomic no (atJwt) will *e of higher priorit!.

eg − CH3 1 − OH 1 − >H2 1 − Cl1 − HC O > Cl H

− Cl A OH A − >H2 A − CH3 A −H.(2) f frist atom same then appl! a*o"e rule on second atoms

CH3

eg −CH31 − CH2 – CH31 − CH 1 − CH2 – rCH3

− CCl3 1 − CHr 2 respecti"el! 3H 2H1 C ? H1 2C? 2H? r ? 3Cl ? H1 2r H C r Cl ?r A Cl A Cl A C A H

CH3

K − CHr 2 A − CH2r A − CCl3 A A − CH2 – CH3 A CH3 CH3 O

eg CHO ⇒ − C – O

− C + O H C

H

⇒ − CHO ? − COOH ? − CH2OH ? − C ≡ > ? − CH2 – >H2

O1 O1 O ⇓ H H H > C H H H

O − C – >

− C – O C > C

OH O1O1O

∴ COOH A CHO A CH2OH A C> A − CH2 >H2

CH3

"# − CH + CH2 1 − C ≡ CH 1 C – CH3 1 − $H ?

8


10/60

CH3

⇒ CisJtrans >omencl.

This method is applied when *oth atom of C + C contain at least one identical group.

CH3 – C + C – CH3 CH3 – C + C – C2 HD

H H H H

f identical group lie on the same side of the C + C *ond then it is called cisJisomer

otherwise trans isomer.

CH3 – CH + CH – C2 HD → 2 – pentene.

CH3 C2 HD CH3 H

C + C C + C

H H H C2 HD

Cis Trans

r Cl r r

C + C C + C

Cl r Cl Cl

Trans Cis

r

C + C sol"ed *! following method.

Cl '

5#L – nomenclature, Top priorit! groups are on the same side then it is called L – isomer

otherwise 5 isomer

r r '

C + C C + C

Cl ' Cl

(L) (5)

This method can *e appl! in all cases of geometrical isomerism.

CH3 CH3 CH3 H

C + C C + C

H H H CH3

Cis#2 Trans#5

H

C + C ⇒ C + C

Cl Cl Cl


11/60

>um*er of geometrical isomers + 2n where n + the no. of C + C *onds. Howe"er if no. of

C + C *ond is e7ual to then no. of geometrical isomers is alwa!s two1 *ut if no. of C +C *ond is more than then no. of geo – isomer ma! *e 2n or M 2n.

i.e C + C + ? %. + 2

C + C A 2 ? %. ≤ 2n

t will *e 2n when num*ering of $.C is not possi*le from either side. On the other hand it

will *e less than 2n1 when num*ering $.C possi*le from either side.

(i) CH3 – CH + CH – CH3 (geo.)

(ii) Cis (iii) trans. + 2.

Cis1 trans Cis1 trans.

↑ ↑

(ii) CH3 – CH + CH – CH + CH – CH 2 – CH2 >o. of geom – isom + (0) sincenum*ering is possi*le onl! from left.

() Cis – Cis () Cis – trans () trans – Cis B ↑ − ↑.

(i) H H (ii) CH3 H

C + C C2HD C + C H

C2HD C + C H C + C

H H H C2HD

Cis – Cis Trans – trans.

H H CH3 H

C + C H C + C C2HD

C2HD C + C H C + C

H C2HD H H

Cis – trans Trans – Cis.

(ii) CH3 – CH + CH – CH + CH – CH3

H H CH3 H

C + C CH3 C + C H

CH3 C + C Cis – Cis H C + C . TransJtrans

H H H CH3

H H CH3 H

C + C H C + C CH3

CH3 C + C . CisJtrans H C + C B TransJCis.

H CH3 H H

and B are identical


12/60

∴ >o. of geo.Jisomer + 3.

(iii) CH3 – CH + CH – CH – CH + CH – CH3

→ C C C

→ T T T

a) C – C – C C – C – C

*) C – C – T T – C – C

c) C – T – C C – T – C

d) C – T – T T – T – C

e) T – C – C C – C – T

f) T – C – T T – C – T

g) T – C – T C – T – T

h) T – T – T T – T – T

∴ >o. of geom – isomers + 6

yclic cases: %eometrical isom. also occurs in rings. ince rotation a*out C – C single *ond of

ring is also restricted.

CH2 – CH – CH – CH3

C2HD C2HD

Howe"er it will *e possi*le onl! if ring *ears at least two groups same or different at

different position.

() (2)

(3) (0) (D)

(6) (I) (;)

(8) ()

(3) or1 ? or1

2

CH

CH3

CH3

CH3 CH3

CH3

CH3

CH3

r

CH3

H

H r

CH3

r

r

r

CH3

CH3

r

r

Cl r

r

r

r

CH3

O

CH3

CH3

CH3

r

H

H


13/60

(D)

oth are identical1 therefore1 no geometrical isomerism in this case.

(I) or1

d + d2

∴ >ote geo – isomers1 since spetial distance does not charge.

Cis Trans.

Cis Trans

***"# ∴ >o. of geo – isomers + 0.

(i) CH3 CH3 OH

C + > ⇒ C + >

C2HD (L) OH C2HD

(Oime)

!neth!l or antimeth!l K %eomJisomers are possi*le.

4 Choose w.r.t hea"ier group.

(ii) CH3 – > + > – CH3 CH3 > + >

↑ ↑ > + > CH3 CH3

CH3

Trans#/nti (∈) Cis s!n(2)

⇒ ntercon"ersion of geometrical isomers , −

3

CH3

CH3

CH3

H

CH3

CH3

CH3

H

CH3 CH3

O(sp2)

HH

HCH3

O

O

p3

H

H

H

H

H H H

H

r

r

r

r

r r r

r

(C#T) r

CH + CH – CH3(C#T)

sp2 sp2


14/60

ince rotation a*out C + C is restricted. ntercon"ersion of geometrical isomers is

possi*le onl! if π − *ond is cleare. This can *e done either *! heating or with the help of catal!st. Nhich can *e an acid or *ase or radicals.

CH3 CH3 / + homo or1 heterol!sis.

(i) (cis) C + C

H H

CH3 CH3 H CH3

C − C C + C

H H CH3 H

CH3 CH3 CH3 CH3

(ii) C + C C + CH H H o H

CH3 CH3 CH3 CH3

C − C C − C – H

H H H

H CH3 CH3

C − C C − C – H

CH3 H H H CH3

H CH3 H CH3

C − C @ H@ C − C @ o

CH3 H CH3 CH3

H.N $ropose mechanism for *ase catah!sed rean

→ ta*ilit! of geometrical isomers, −

That geometrical isomers will *e more sta*le in which steric – repulsion is less.

CH3 H CH3 CH3

C C

H CH3 H H

Trans Cis

CH3 CH3

0

• •

H@


15/60

H C

H C2HD C + C CH3

C + C CH3 C2HD C2HD

C2HD C

CH3 CH3 Trans M Cis

→ elting point of geometrical isomers

'2()1 Cl2()1 r 2()1 2 (δ)

i.e intermolecular force of attraction

2 A r 2 A Cl2 A '2

$olarisation of e− clad.

eg C + O

C OH

CH3 – CH2 – CH2 – CH2 – CH3

CH3 – CH2 – CH2 – CH2 – CH3 n pentane ntermolecular "ander walls force of alterationis more in n – pantane that in new pentane

ntermolecular "ander walls force of alteration (for single molecule) is more in neoJpent.

Than in n – pertane. Therefore newJpentane is more sta*le than nJpentane.

CH3 CH3

CH3 – C – CH3 CH3 – C – CH3 >eoJpentane

CH3 CH3

CH3 CH3 CH3 H

C + C C + C

H H H CH3

(Cis) ⇓ ⇓ (Trans)

CH3 CH3 CH3 – CH + CH – CH3

CH + CH map

map

D

δ@

δ@δ−

δ−

δ@ δ−


16/60

intermolecular "ander walls force of attraction is more in trans isomer than in cis.

Therefore map of trans 2 – *utane is more straight than that of cis.

Solubility

CH3 – OH

OH H

H

CH0. O

H

olu*ilit! of cis – isomer is more then that of trans – isomer.

Optical isomerism:

$lane – polarised light, Ordinar! light "i*rates in all dir n1 when pass to a nicol prism

(ade up of CalO3)1 it *egins to "i*rate in onl! one dir n

. Then it is called plane polariedlight.

>o effect or. Compd (inacti"e) /cti"e(opticall!)

Optical isomerism is the isomerism which deals with opticall! alti"e compds. Howe"er either all optical isomers will *e opticall! acti"e or some ma! *e acti"e and some

inacti"e.

/s!mmetric centre # chiral centre

The C – atom *earing for different group is called as!mmetric or chiral centre.

CH3 – CH – CH2 – CH3 CH3 – CH2 – CH – CH2 – CH2 – CH3

r 4 C + . r

6

H2OH2O

OH2

H2OH2O

H2O

OH2

>a@

OH2

Cl

OH2

H2OH2OH2O

H2O

H2O

>icol prism

ample tesle containing

Org. compd.

&ight ward

detro. lea"o.

left ward

Compd

OptJacti"e Opt –inacti"e

-etrorotator!

d or (@)

ea"orotator!

l or (−)

∗ ∗

∗∗


17/60

CH3 – CH – CH – CH3 CH3 – CH – CH – CH3

r r r Cl

4 C + 2 (imilar) 4 C + 2 (dissimilar)

r

CH3 CH H C + C C + C

H H H CH3

cis trans 4 C + .

4 C + . 4 C + O 4 C + O 4 C + O 4 C + .

4 C + 2 (similar) (C4 + 2) C4 + O.

→ $resentation of as!mmetric C – centre and configuration.

(i) 'ischer pro=ection formula, −

COOH COOH CH3

CH3 – CH – C2HD CH3 C H ≡ CH3 H ⇒ HOOC C2HD

COOH C2HD C2HD H

to 3 "ia – 2 H CH3

Clock wise – & C2HD COOH H C2HD

/nti clock – . CH3 COOH

>ote, That this str. ha"ing same configuration on all respecti"e ass!metric centre will *eidentical.

CH3 CH3

H OH OH H

H OH H OH

C2HD . C2HD

H H

I

∗

OH OH OHOH

O

∗

OH

O

CH3

∗∗

CH3 ∗

∗

CH3

CH3 CH

3

CH3

2

3

&

&

&

&


18/60

OH OH CH3 H

OH C2HD C2HD OH

H B OH

and are identical

and are identical and are identical

and are identical

and B are identical

and B are identical

CH3 CH3

(i) H OH (ii) HO H

H OH H OH

C2HD C2HD

CH3 Cl CH3 Cl

H OH H OH HO H H OH

Cl C2HD Cl C2HD

OH OH H OH

Cl CH3 C2HD Cl Cl C2HD C2HD Cl

H H OH H

H H CH3

() OH CH3 HO CH3 Cl H

OH C2HD Cl OH

H

H Cl

CH3 OH ⇒ HO CH3

Cl HCOOH COOCH3

2 H OH H OH

H OH H OH

COOCH3 COOH

OH

;

&

&

&


19/60

COOH OH − CH

H OH Cl COOH ? COOCH3

Cl H O

C O

OH C

oth are non – identical.

In 'e%ge formula:

CH3 – CH – COOH

OH

H CH3 COOH OH CH3 C2HD

C ⇒ ?

OH COOH CH3 H OH H

In sa'horse formula:

This formula is written it molecule has two#more ass!m. centre

CH3 – CH – CH – C2HD

OH OH

CH3 H OH

H

OH C2HD

H C2HD

Cl OH "ertical *ond ⇒ OH Cl

C2HD H

CH3 C2HD CH3

CH3 OH ? OH CH3 Cl

H H H OH

H OH CH3 Cl

Cl OH

CH3 H

8

CH

OC

∗

∗ ∗

s&


20/60

OH C2HD H

and &

H CH3 OH

Plane of Symmetry:

f molecule can *e di"ided with two e7ual portions – One portion *eing the mirror image

of the other portion then it is said to ha"e plane of s!mmetr!.

/ molecule without plane of s!mmetr! is called diss!mmetric. >ote that all the

s!mmetric molecules are opticall! inacti"e.

CH3 ∴ Has plane of s!mmetr!

H OH ∴ opticall! inacti"e.

H OHCH3

CH3 → >a plane of s!mmetr!

H OH ∴ olecule is diss!mmetric and thus opticall! acti"e.

HO H

CH3


21/60

)onsuper impossible Super impossible

→ /ll diss!mmetric molecules ha"e → /ll s!mmetric molecules ha"e super

nonJsuper impossi*le mirror image impossi*le mirror image

→ There structures will *e non – super impossi*le mirror image of each other in which

configurations are opposite on all respecti"e as!mmetric centres.CH3 CH3 CH3 OH

H OH HO H H OH H CH3

H r r H H r r H

CH3 CH3 CH3 CH3

-iss!mmetric

∴ P one nonJsuper impossi*le mirror ∴ oth nonJsuper impossi*le mirror

image of each other image of each other.

→ Condition for optical isomers, −

(i) $resence of s!mmetric centres, −

f a molecule at s!mmetric centre then optical isomerism certainl! occurs. Howe"er there

are molecules which do not ha"e an! as!mmetric centres *ut ehi*it optical isomerism.

(ii) presence of diss!mmetr!, −

olecule with diss!mmetr! are alwa!s opticall! acti"e therefore ha"ing diss!mmetr! is

the compulsor! condition to ehi*it optical isomerism

>o. of optical isomerism + 2n

Nhere n + no. of ass!m. centre

Howe"er in some cases no. of optical isomerism will *e less than 2 n. These cases will *e

the cases of similar as!mmetric centres.

∴ C4 + – >o. of optical isomer + 21

dissimilar C4 + 2 similar

>o. of isomer + 0 >o. of isom + 3

CH3 – CH – COOH

OH

COOH COOH

H OH OH H

CH3 CH3

oth are acti"e and called enantiomers.


OH r

2

&

&

∗

∗ ∗


22/60

CH3 CH3

H OH HO H / pair of enantiomers.

H r r H

I CH3 II CH3

CH3 CH3 HO H H OH / pair of enantiomers.

H r r H

III CH3 I+ CH3

>o. of optical isomers + 0.

is diastereomers of – and B.

is diastereomers of and .


r r

CH3 CH3

H r r H and → identical called

H r r H mesomer.

CH3 CH3

CH3 CH3

r H H r >O. of isomer + 3 *ecause

H r r H and are identical

CH3 CH3

oth are pair of enantiomers.

⇒ 'eatures of enantiomers, −

(i) Those two str. are enantiomers of each other which are non – super – impossi*le mirror

image of each other.

(ii) Those two structure are enantiomers of each other which ha"e opposite configuration on

all respecti"e centres.

(iii) 5nantiomers are alwa!s diss!mmetric and there opticall! acti"e. One will *e

detrorotator! while other lea"o. *! same magnitude.

COOH COOH

H OH HO H

CH3 CH3

@ 2o − 2o

− 0Do @ 0Do

22

∗∗


23/60

(i") /n e7uimolar miture of enantiomer is called recemic miture1 recemic mi are

opticall! inacti"e due to eternal compensations.

(")

Mesomer:

(i) Opticall! inacti"e isomers is called mesomers

(ii) t is found onl! in cases of two or more similar as!mmetric centres.

(iii) That isomer will *e mesomers which has plane of s!mmetr! conse7uentl!1 its mirror image will *e super impossi*le.

(i") That str. will *e mesomer in which configuration are opposite on similar as!mmetric

centres within the molecules.

This is the reason that mesomers are opticall! inacti"e.

CH3 CH3

H r r H

C2HD C2HD

(@ 3) (− 3)

CH3 @ 0o

H OH

H OH

CH3 − 0o

esomers are opticall! inacti"e is detro while other half is lea"o *! same magnitude.

,iastereomers:

→ Those isomers are diastereomers which are not mirror image of each other.

→ The two str. which are neither identical nor non enantiomers are diastereomes

→ /ll chemical and ph!sical prop. of diastereomes are different.

On the other land enantiomers ha"e all ph!sical properties same ecept their entraction

with plane polaried light which in e7ual and opposite.

The! all chemical properties of enantiomers are same ecept their reacti"it! with chiralreagents.

→ %eometrical diastereomer.

C2HD C2HD r r

H r r H H C2HD C2HD H

23

&

&

&

&

&


24/60

H OH CH3 HO HO CH3 HO CH3

CH3 H H H

B

P – P B → enantiomer

P – P – P B → diastereomes P B – identical.

". COOH COOH

H CH3 CH3 H

C2HD C2HD

enantiomers.

This order doesn:t match with eperimental order. Howe"er onl! the position of

c!cloheane is delocated i.e theor! faith of c!cloheane cense of this failure is the

assumption that all rings are planer. ut c!cloheane is not planer. t eist in chair and *oat form mainl!.

h!pothetical Chair oat

form /ll age form + 8o 2;:

∴ /s + O

mp + mp ? p + p

solu*ilit! + solu*ilit!& + & .

*ut @2o − 2o # − 2o @ 2o

COOH COOCH3

H r H r

CH3 CH3

and

COOH COOCH3

r H r H

CH3 CH2

∴ Q + Q 2

f reagent is chiral such as

CH3

HO H then Q ≠ Q 2

20

Q

CH3OH#H@

Q 2

CH3OH#H@

2o


25/60

O


26/60

% + 2 % + 2 % + 2 % + O + 0 O + 3 O + 0 O + 2

& m + & m + 2 & m +

eso +

Trans dl – pair Cis dl – pair

-# – configuration, −

CHO CHO

H OH OH H

CH2OH CH2OH

- # (@) %l!cerol # (−) %l!cerol

i.e (@) %l!cerol is assigned - – configuration while (−) %l!cerol is assigned – configuration assignment is ar*itrar!

!lyceric (ci% :

CH2 – CH – COOH

OH OH

f - – gl!cerol is o*tained then configuration is gi"en gl!ceric acid was - and it –

gl!cerol o*tained then configuration in gl!ceric acid was li.

!lycerol : similar configuration &etension # n"ersion in configuration.

&etension occurs if reagent attack from the front side and in"ersion occurs if reagent

attacks. 'rom the *ack side.

CH3 CH3 CH3

H r → −OH H OH @ OH H

C2HD CH3 C2HD

&etension prd n"ersion prd.

Inversion also calle% -al%en.s inversion Erythro – threo nomenclature:

26

CH3

CH3

CH3

C2H

D

CH3

H

H

C2H

D

CH3

H

HC2H

D

CH3

H

H C2H

D

CH3

H

HC2H

D


27/60

This nomenclature is applied when molecule has two dissimilar ass!metric car*on atom

containing two similar group.

CH3 – CH – CH – C2HD. CH3 – CH – CH – C2HD

OH r OH OH

f similar group are same side in fisher pro=ection formula then it is called sr!thro isomer

otherwise threo isomers.

CH2 CH3

H OH HO H

H OH HO H

C2HD C2HD

5r!thro – dl – pairs

CH3 CH3

H OH HO H

HO H H OH

C2HD C2HD

Threo – dl – pair

⇒ Optical isomerism without C4

Case of cumulenes

CH3 CH3

C + C + C

H H >onJplaner

The molecule is dis – s!mmetric therefore opticall! acti"e.

>o. of optical isomers + 2

CH3 CH3 (planer) s!mmetric

C + C + C + C (>o opticall! acti"e)

H H

CH3 H not planer s!mmetric

C + C + C >o optical acti"it!.

H H

umulenes

→ 5"en no. of C + C optical isomerism → Odd no. of C + C geometrical isom.

occurs and if each *ears two different occurs if each and e"er! *ears two

2I


28/60

groups different groups.

ase of biphenyles:

iphen!l ehi*its optical isomerism if ortho su*stituent are present and *oth ring are

opticall! diss!mmetric.

dis!metric opticall!acti"e O + 2

!mmetric >O. O – .

Resolution: eperation of enantioment or recemic mi is called resolution

That since ph!.prop of enantiomers are same the! can not *e separate *! ordinar!methods like fractional distillation or c!otellisation. Howe"er it is possi*le throughcon"ersion cnto diastereomers.

CH3 C2HD

H COOH ? H COOH

C2HD CH3

$HH@ HO H

-

O $H C2HD O $H

H C – O H ? H C – O H

O CH3 -

H3O@ H3O

@

- -2

'ractional distillation

CH3 $H

- + H COOH @ HO H

C2HD -

C2HD $H

-2 + H COOH @ HO H

2;

r r

r


29/60

CH3 -

O

4 &COOH @ CH3OH → + )( H & – C – CH3 G H3O

@

↓

&COOH @ CH3OH

⇒ Conformational isomerism, −

>ew man pro=ection formula , −

>ew man taggred form

5lips formula

4 -ihedral angle , − interplaner angle is called dihedral angle defined *!

-ihedral angle tg. eclipsed

H – C – C – ' – ; 2

H – C – C – r – 6 2

H – C – C – Cl – 6

Condition for conformational iso.

28

a

a

*

*c

c

c c

l l m m

n

n

a

* c

l

mn

'

Cl r

OHH

'

OH

HCl r

a – * – c – d

a

d

*

c

a

d c

*

;o


30/60

olecule must ha"e an unit like a – * – c – d and rotation should *e free. >o. of

conformers will *e infinite and a d!namic state of egutn. The! are not *e separated.

>H3 H H

>

H

H2O H H

CH3OH C + C

H H

H – O – O – H

CH3 – CH3 CH2 + CH – CH2 – CH3

Conformational anal!sis of ethno.

taggred form 5clipsed form

>o. .$1 prepulsion, $ – $ – repulsion

2 . 6 Qcal # mol

&otation # di"edral angle.

4 Heat of com*ustion is sta*ilit!.

&H @ O1 → CO2 @ H2O @ Heat

Rsing heat of com*ustion relati"e sta*ilit! can *e deri"ed if molecular formula is same

CH3 – CH2 – CH2 – CH3 2

.3O2 → HCO2 @ QCal#mol

CH3 – CH – CH3 @2

.3O2 → HCO2 @ 3H2O @ !QCal#mol

CH3 F A !G

Therefore iso*utene is more sta*le than H – *utane

→ &ule is that *ranched alkane is more sta*le than un*ranched.

∆H#CH2

3

H

H H

H

HH

H

H H

HH H


31/60

66.6 DI.0

60.

D;.I

,eyer.s strain theory :

/ngle strain +2

S2;H8 eactualangl o − P sta*ilit! ∝ #angle strain

/ngle strain1 +2

6HS.;.H8 −o

+ 20o00′

+ S0082

8HS2;H8 oo

=−

+ S002

H;S2;H8 =− oo

+ S00D2

H;S2;H8 oo

−=−

∴ sta*ilit! order on the *asis of angle strain is

This order doesn:t match with eperimental order. Howe"er onl! the position of

c!cloheane is delocated. t means that this theor! fails at c!cloheane cause of failure isthe eemption that all! ring are planer. ut c!cloheane is not planer. it eist in chair and

*oat forms mainl!

H!pothetical ? /ll angle + 8o 2;′

train + .

** onformation analysis of butane – /0 – /& – /0

() /nti form () $artiall! eclipsed.

3

2o

H

H H

H

H

HH

6o

6o

CH3

CH3CH3

CH3

H

CH3

CH3

H

HHH

CH3

CH3

H HH

H


32/60

() %auche (B) 'ull! eclipsed.

() /nti form , − >o $ – -$ repulsion >o steric # "enderwall repulsion ? (ost sta*le)

() $artiall! eclipsed , −

→ $ – $ repulsion

→ ome "enderwall repulsion

() >o $ – -$ repulsion some steric repulsion

(B) -$ – $ repulsion on man steric repulsion

Stability or%er :

/nti A %auche A $artiall! eclipsed A full!ed

5nerg! profile , −

Subtituent effects:

u*stituent /cidit!

The atom or group which itself doesn:t participate inren *ut effect reacti"it! of themolecule is su*stituent and its effect is called su*stituent effect.

-epending upon the modes of transmittance su*stituent effect is classifies as

u*stituent effect nducti"e steric

32

/nti /nti%auche

'ull! eclipsed

$artiall! eclipsed

-ihedral angle

$5

OH OH

>O2

>O2

>a@ >a@O− O−

@H2O@H2O

− &eadil!.

>aOH >aOH


33/60

→ mesomeric

→ H!percon=ugation

→ electromeric

/ypercon1ugation :

Transmittance of su*stituent effect through σ − π con=ugation is known ash!percon=ugation. t occurs in

(a) /lkenes. (*) /lk!nes. (c) Cations. (d) &adicals.

$ro"ided that – there is at least one h!drogen at the con=ugated position.

p3 CH2 – CH + CH2 ≡ H2C CH – CH2

H p2 p3

CH2 – CH – CH2

H@ ≡ CH2 – CH – CH2

⇒ Nrite structures in all and h!percon=ugation, −

CH2 + CH2

CH3 – CH + CH – CH3

CH3

C + CH – CH2 – CH3

CH3

CH3

CH3 – CH2 ↔ CH2 – CH2 ↔ CH2 + CH2

H H

CH3 – CH – CH2 – CH3

CH3 – CH2 CH2 – CH2 ↔ CH2 + CH2

H H

CH3 – CH – CH3

→ n the structure arising from h!per con=ugation are C – H *ond is clea"ed. That is wh!h!per con=ugation is also called no *ond – resonance.

→ Total no. of structures will *e e7ual to no. of h!per con=uga*le H atom @ .

33

Hσs

H@

••

• •

•

•••


34/60

Howe"er these structures are imaginar! or real.

Ha

H * C – CH + CH2 → CH2 + CH – CH2

Hc Ha

CH2 + CH – CH2 CH + CH – CH2

Hc H *

Haδ@

H *δ@ C – CH – CH2

δ−

Hcδ@ H!*rid.

/s shown C – H *ond is actuall! not clea"ed *ut elongated such that C – H *ond pair electron are shifted more towards car*on.

Therefore h!per is a method of electro – donation n other words an alk!l group donates

electron *! wa! of h!per and this e−

− donating power is directl! proportional to no. of h!per con=uga*le H – atoms.

CH3 CH3

− CH3 A − CH2 CH3 A − CH A − C CH3

o 2o CH3 CH3

(Lero no. of H – atom)

CH3

CH2 + CH – C CH3 → (+) *ond is added

CH3

Therefore in general1 electron donating power of alk!l groups through h!per con=ugation

is

− CH3 A o & A 2o & A 3o &.

ince h!per con=ugation in"ol"es delocalisation of e− it increases sta*ilit! of the

molecules

CH2 + CH2 H

CH3 – CH + CH2 3 H

CH3 – CH + CH – CH3 6 H

B CH3

C + CH – CH3 8 H

30


35/60

CH3

B. CH3 CH3

C + C 2 H

CH3 CH3

ta*ilit! B A B A A A &ule is that more su*stituted alkene is more sta*le than less su*stituted alkene.

/ypercon1ugation is heat of hy%rogenation :

5tent of heat of h!drogenation ∝ #etent of h!percon=ugation

∴ Order of heat of h!drogenation is

A A A B A B.

CH3 – CH3 – CH2 – '

⇒ agnitude of – effects

@ − O

− COO – CH2 – -

(i) − O A − COO A − CH3 A -

(ii) − >O2 A − '

(iii) − A − OH

O

C AAA > → O ?3

+

NH A − >O2

444 / general order of − : magnitude – >H3 A − >O2 A − C> A − COOH A − ' − Cl A − r A − A OH.

− CH3 @ – effect.

CH3 CH3

− CH2 – CH3 − C(CH3)3 A − CH A − CH − CH2 – CH3 A − CH3

3o CH3 2o CH3

o

CH3

− C – CH3

CH3

∴ %en. order of magnitude of @ effect among alk!l group is 3o A 2o A o CH3

)ote : that this order is =ust opposite to the order of e− donating power through h!percon=ugation

which is ml A o A o A 3o.

3D


36/60

⇒ esomeric effect or (&esonance effect)

Transmittance of su*stituent effect through π − *ond is called mesomeric effect (#& – effect) therefore this effect operates onl! in molecules undergoing &esonance.

CH2 + CH – O CH3 → su*stituent.

CH2 – CH + OCH3

– effect

( @ ) (− )

→ f su*sti. donates a pair of e− → f su*sti. withdraw π − e− in

in resonance. uch grps one called π − donar resonance. uch grps are called π − accepter

eg , − O CH3 ( @ 1 − )

− >H2 (− 1 @ )

− >O2 (− 1 − )

− (− # @ )

− C> (− # − )

− COOH (− # − ) ? − CHO (− # − )

− CH + CH2 @ # − − ? − >O

− COCl (− # − ) − N + O

− COCl (− # − ) @ − # − .

− COO& (− # − )

− C ≡ CH − @ # − # −

− $H @ # − # − .

eg ,

@ # − ≡ E

@ A A

− A A .

eg, O

O CH3 1 – O – C − CH3 1 – O – CH + CH2

36

>O2 O CH3


37/60

@ − A A

O CH3 A − $H ? − CH + O A $H

@ @ − −

O O O

− C – H − C – >H2 − C − O CH3

− ? A A .

!roups

− # − @ 1 @ (−O) − # @

i.e σ − accepter as well as π −accepter

/ccepter

i.e σ − donar as well as π −donar i.e donar σ − accepter π − donar *otheffectance operating then

mesomeric effect is fa"ouredtherefore such groups

effecti"el! acts as donar

: Electromeric effect :

$olarisation of π − *ond caused *! the approach of reagent

eg. CH2 + CH2 → / non – polar *ond.⇓ H@

@CH2 – CH2

H

Therefore this effect is temporar! and operates onl! in ecited state.

: (l2one :

3I

COOH

OCH3− # @ ∴π − donar

COOH

>O2 − # − /ccepter


38/60

Preparation :

() C + C → 2,# NH N C – C @ ∆H

− C ≡ C – → SS C – C @ ∆H2

E3othermic :

C + C → 2 H C – C @ ∆H (wrong)

5act of h!drogenation + high so a catal!st is regd to lower the eact

atalyst

/omogeneous

&hCl ($$H3) chlorotris – triphen!l plusphine

rhodium1 or willkinson catal!st.

/eterogeneous

&ame! >i1 pt1 pd (p – 2) lindlar catal!st

Alloy

Al Ni )( + worom

agNaOH → &ane! >i &a! – >i finall!

di"ided into >i – $articles

→ p – 2 is >i2 (>ickel *oride)

B NiOAC Nieborohydrid sod

NaBH

aectate Nickel 2

).()(2

0)( →

→ indlar:s cat. is pd#aO0#


39/60

C + O →

U CH – OH

& &

O

& – C – O & ′ → &CH2 – OH @ & ′ − OH

& – C> →

U &CH2 >H2

& – COCl →

U & CH2OH

& &

C + > – OH →

U CH – >H2

& &

& – CH + O

H ↓ H

& CH2 – OH

O

& – C – O – & ′ → 2# H Ni

& CH2

OH @ & ′OH O

& – CH – O& ′ → & – CH + O@ @ & ′OH

>i#H2

& – CH2 – OH

OH

C → C + >H @ H2O

>H2

O OH

& – C – >H2 → NI H #2 & – CH – 2

..

H N

& – CH2 – >H2 ← 2# H Ni & CH + >H ←

+− H & – CH + >H2

/n ester , −

(i) ester E → Ni H #2 OH + CH3 – CH – CH3

o OH

38


40/60

O

/ns $H – C CH3

O – CH

CH3

(ii) ester E → Ni H #2

C + O

mp. O

& – C – O & ′ → o # 2o # 3o

& CH2OH onl! o (alwa!s)

E How man! esters → 2# H Ni CH3 OH @ C2HDOH

o o

/ns O O

H – C – O C2HD # CH3 – C – O – CH3

E How man! h!drocar*ons for2I

2#

H C For

H Ni →

/ns

→ H!drogenation → s!n radical addition

C + C

H H

catal!st cis1 meso onl!

&eacti"it! !ne A ene:

JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ

CH3

(ii) CH2 + CH2 A C + CH2

CH3

0

OH

OH

2o

o

OO

CH3

CCCC

CH3

CH3

CH3

CH3

H

H


41/60

SE4E5I+I56

(willkinson:s cat)

& – C ≡ C – &

↓ p – 2

& – CH2 – CH2 – & & &

C + C

H H

(onl! cis) so *oth p – 2 and – cat are selecti"e rid – agent of ≡ # +.

44 & – C ≡ C – &

(nice) echanism , − i → i⊕ @ e−

& – C ≡ C – &

↓ &

& – C + C – & ≡ C + C

&

JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ

& H

C + C

&

↓ >H3

& H

C + C

H &

→ ! di"ide (H> + >H)

(h!drogine) >H2 – >H2 → 22O H H> + >H (di"ide)

H H

> + H onl! cis di"ide is used for h!drogenation

0

CH + O CH2OHCH2OH

>aH0 >i#H2

CHOo1 wiliumson:s

aplnopriste forgenation of

cat (wc) is selecti"e

h!dro C + C *onds.

>i#H2

indlar:s catal!st

C + C (Trans)&

H &

H

C + C (cis )

&

H H

&indlar:s

Catal!st

#>H3

•

•


42/60

→ ! h!dro*oration ,− H2C + CH2

↓ H3 , TH' (T H ')

ech

CH3 – CH2 CH2 + CH2

H –

→ 5lectrophilic addition.

→ arkonico" rule is o*e!ed.

→ !n addition.


43/60

Called irch reduction which gi"es 1 0 c!cloheadiene not 1 3 c!cloheadiene e"en

though ca*er is more sta*le than former. Came (not clear)

→ Qol*e – electrol!sis

& – COO>a → is Electrolys & – &

mech

O

& – C – O− >a@ O

/node , & – C – O• @ e−

Cathode , >a@ @ e− → >a

>a @ H2O → >aOn @ V H2↑

O

& – C – O → & • @ CO2

2& • → & – &.

/s reacn mo"e pH of soln inc. due to the formation of >aOH.

CH3COO>a → −e CH3 – CH3

→ -ecar*o!lation of fatl! acids.

CH3COO>a >aOH # CaO # odaline

O

∆ ↓ sodaline CH3 – C → CH3 @ CO2 → )( 2O H CH0 .

CH0 C

Car*anion is the intermediate therefore e− withdrawing grp. increases the ease of

decar*o!lation

. CH3 – COOH

. CH3 – CH2 – COOH

. CH3

CH – COOH

CH3

ease , A A .

Qe!, Wust remo"e CO2 ↑ from compd.

O O O

CH3 – C C – OH → ∆ CH3 – C – CH3

CH2

CH2 – COOH → ∆ CH3 – COOH →

sodaline C – H6

03


44/60

ech, O O O

CH3 – C C – OH → CH3 – C – CH2 @ CO2 CH2

O H – O

CH3 – C C + O O CH3

CH2 C

∆ ↓ OH CH3

CH3 – C + CH2 @ CO2

O

COOH C

CH2 → CH2 O

COOH H

C + O

OH O – H O

CH2 + C @ CO2 → CH3 – C – OH

OH

→ Nurt reaction , & – ∆ → ether Na #

& – &.

ech , & – → Na & >a @ >a

& – → & – & @ >a

o 1 2o 1 3o halide undergo this reacn. >ot 3o due to JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ

CH3 CH2 – H CH3

CH3 – C – → Na CH3 – C → C + CH2

CH3 CH3 CH3

n wurt reacn onl! that alkane is formed in good !ield which re7uires onl! one & –

which is net 3o.

CH3 – @ CH3 – CH2 –

↓ >a

CH3 – CH2 – CH3 @ CH3 – CH3 @ CH3 – CH2 CH2 CH3


45/60

CH3 – CH2 – CH2 – CH2 – CH2 – CH3

CH3 CH3

CH3 – C – C – CH3

CH3 CH3

→ 'rankland reacn

,− ller as wurt ecept >a is replaced *! Ln.& – → Zn & – Ln – → − I & – & @ Ln2

↓Ln

& – &

→ Core! house alkane s!nthens ,−

→ *etterthan wurt.

& – → !i & i

↓ Cu

& – & ′ ← & 2Culi @ & ′

eg CH3 – CH – CH2 – → CuliCH CH 223 )( CH3 (CH2)3CH3

→ 'rom %rignard reagent & – → ∆ Ethen Na # & – g – (%J&)

44 own & – g –

i.e compd H O H → 2

relearning H@ H NH → 3

will gi"e &–H H OH CH → −3

with %J& H NH − → − 2

H COOH CH − → 3

D DiO →

() CH3 – CH + O + → H

"gx

.2

.

CH3 – CH – OH

&

CH3 CH3 OH

(2) C + O+

→ H

"gx

.2

.

C

CH3 CH3 &

O

(3) CH3 – C – OCH3 + → H excess "gx )(

CH3 – C – &

&

0D


46/60

(0) +

→ H

"gx

.2

.

O O

(D) $H – C – OCH3 ).( g "gx → $H – C – &

own nfact %& @ H@ → alk.

o in reacn not add

& H@ or multiple *ond for product

H0 Cl

OH

C2HD – C – $h @ CH3OH

$h

/ns /ns O

CH3 – CH2 – C – OCH3

CH3


47/60

O OH

& – C – OCH3 −−−−−−−−

→ .2

. 3 "gBr CH & – C – CH3 @ CH3

O

& – C – O& ′

OH CH3OH

& – C – CH3

CH3

mp. O

& – C – O& ′

3o alc. o1 2o1 3o

>ote, That %.& can:t *e prepared from i.e. dilalids. added to this it can:t *e prepared if molecule contains one or more reacti*le group.

r r

CH2 – CH2 CH2 – CH2

r ↓ mg g

CH2 + CH2

eng!ne.

H0Cl ↓ CH3 g r (ecess)

OH

CH3 OH @ CH3 – CH – CH3

/ns O

H – C – O CH3

→

∴

0I

r

r

r

r

g

>H2Cl

>a>H2

Cl

>H2

or1 p2

H


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→ Clemenson and wolf kishner reduction

(ket or ald.)

&

mech, (w.k red) (i) C + O @ 3 H N

&

& OH & O

C C

& 2..

H N & >H3

& &

C + >H2 C + >H

& &

)ote, − C& – acidic med. oth are complementar! to each other

wk – *asic med.

i.e t ketone # ald gas acid JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ

carried at1 it *ase semiti"e then C& is carried out

& H &

(ii) C + O @ > – >H2 → C – H2

& H (h!draine) &

& &

C + > – >H2 @ H2O C – H @ >2

& ↓ QOH &

& &

C + > – 2 H N − CH – > + > @ H2O

& & ↑ QOH

& &

C – > + >H → O H 2 CH – > + >H

& &

0;

Ln#HgA CH

2

A CH2∆ >2H0QOH (N.Q)

C + O

pure

(an!)


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Properties :

/alogenation :

& – H @ 2 → heat !ight # & – @ H

mech,− – → ∆ 2 • (i)

• @ H – & → sd r .. H @ & • (ii)

& • @ – → & @ • (iii)

&elati"it! of 2 → '2 A Cl2 A r 2 A 2

&elati"it! of H – atom 3o H A 2o H A o Cl

K 3o & A 2o & A o &

electi"it! , CH3 – CH2 – CH3

↓ Cl2 # light

CH3 – CH – CH3 @ CH3 – CH2 – CH2

Cl D69 (ma=) 009 Cl (min)

electi"it! ratio + &eacti"it! × pro*a* ratio

3o H 2o H o H

Cl2 D , 3.; ,

r 2 6 , ;.2 ,

electi"it! ratio + .#326.3

;.3

6

2

;.3 II ===×

@ + 9

∴ 9 + D69 9 + 009

CH3 – CH2 – CH3 → light Br #2 CH3 – CH – CH3 @ CH3 – CH2 – CH2 – r

08

Ln # H

Conc HCl

>2H

0#OH

O

OH

Cl

Cl

>2H

0#conc QOH

Ln # H

conc HCl

O

OH

OH

Cl


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r 869 09

/ll H – atom of alk. Can *e replaced

CH0 → ∆#2Cl CH3Cl → CH2Cl2 → CHCl3 → Cl

CH3Cl (e=)

CH0 (5l.) @ Cl2 (ee)

CCl0 (a=)

"# CH3 – CH3 → ∆#2Cl How man! prd.

/ns + 8.

ombustion : Heating alkanes in atm. Of O2

CH0 @ 2O2 → ∆ CO2 @ H2O @ heat

CH3 – CH3 @ 8#2 O2 → 8 2CO2 @ 3H2O @ heat

n asscence of sufficient amount of O2 in complete com*ustion occurs

CH0 @ 3#2 O2 → CO @ 2H2O

CH0 @ 3O2 → C @ 2H2O

amp *lack.

Pyrolysis: Heating alkanes in total a*sence of O 2 is called p!rol!sis or cracking which

produces lower alkanes from higher ones

CH3 – CH3 → 2 . CH3

↓ DoC

CH0

(47E)E

Preparation:

() 'rom alcohol,

〉 C + C 〈 +

←orH

$O H 02 〉 CH – C 〈 → HCl 〉 CH – C 〈

OH Cl

Case, − Cl− is much *etter nu than HO0−

mech, 〉 CH – C 〈

OH

↓ conc H2O0

H

〉 C – C 〈

5 OH 52

D


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〉 C – C 〈 〉 C + C 〈

HO0 H → 〉 C + C 〈 @ H2O0.

o alc follow 52 pathwa!1 while 2o and 3o alcohol follow 5 pathwa!.

Cause , o C is not so sta*le.

CH3 – CH2 – CH2 – CH2 – OH

∆ ↓ H2O0

CH3 – CH2 – CH + CH2 CH3 – CH + CH – CH3 CH3 – CH2 – CH2 – CH3

↓ H (a=or) ↓

CH3 – CH2 – CH – CH3 CH3 – CH2 – CH – CH3

How man! products

JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ

CH3

CH3 – C – CH + CH2 @

CH3

CH3 CH3

CH3 – C + C @ CH2 + C – CH – CH3

CH3 CH3 CH3

OH → ∆+ # H @ a=or

: Pinacol – pinacolone rearrangement :O

& – CH – CH – & → $O H 2 & – C – CH2 – &

ech, H

& – CH – CH – & → ⊕

H & – C – CH – &

OH OH OH OH2

O H

& – C – CH2 – & ← ⊕

H & – C – CH – &

O – H

mp. igrator! aptitude,

H A $H3 A 3o & A 2o & A o & A CH3

$H CH3 $H O


52/60

o C@ ion rearrangement

→ Laise" rule is followed for orientation

→ t is not re"ersi*le *ecause H is neutralied *! *ase.

5, 'ind the ma=or product

CH3 – CH – CH2 – CH3 ∆

→ kon Alc.

CH3 – CH + CH – CH3

r

r


CH3 ↓ /lc. con1 ∆

D2


53/60

CH3

rkon

Alc → C + CH – CH3 (a=)

CH3

ecause path is 52 in which there is no C@ rearrangement.

: ,ehalogehation :

r

Ln 〉 C – C 〈 Q

r ↓ g

〉 C – C 〈 〉 C + C 〈 (a=) 〉 C – C 〈

@ Lnr 2 @ gr 2

echanism , −

r r r

〉 C – C 〈 〉 C – C 〈 〉 C – C 〈

r r r

↓ Ln ↓ g − ↓

r r r

〉 C – C 〈 〉 C – C 〈 〉 C + C 〈

Ln r ↓ g r @ r @ Qr.

〉 C + C 〈 @ Ln r 〉 C + C 〈 @ g r 2

Imp# r

〉 C + C 〈 *ut 〉 C – C 〈 → 〉 C + C 〈 @ 2

r (sta*le) (not sta*le)

r

"# CH + CH – r → Zn HC ≡ CH

r → Zn

r r

→ Zn

r

mp.


54/60

C + C

$H r

$H

↓ Ln C + C$H

$H – C ≡ C – $H


55/60

Case, H is strongest acid and − is a good >u−

Cl

CH3 – CH – CH + CH2 → HCl

CH3 – C – C2HD *oth enahtiomer

CH3 CH3

Cl

and CH3 – CH – CH – CH3 (a=or)

CH3

9PERO8I,E EFFE5

CH3 – CH – CH3 ← HBr CH3 – CH + CH2

22O

HBr → CH3 – CH2 – CH2

r r arkon – addition /ntimark – addition

& – O – O – & → ∆ 2&O•

&O• H – r → &OH @ r •

CH3 – CH + CH2

(2) ↓ r • ()

CH3 – CH – CH2 () CH3 – CH – CH2• (.)

r H r r

CH3 – CH2 – CH2 @ r •

r

$eroide effect works onl! on Hr not on HCl and H.

Cause, oth step () and (2) are eothermic in case of Hr not in case of H and HCl now peroide effect separates also on other t!pes of molecules like CCl01 CHCl3. Cr 3 etc.

5,J Cl

CH3 – CH + CH2 OCCl → 0

CH3 – CH – CH2 (not formed)

↓ CCl0 . peroide

CH3 – CH – CH2 – CCl3.

Cl

Cause,J first • CCl3 attacks

& – O• @ Cl – CH3 → & – OCl @ • CCl3

DD


56/60

& – O – CCl3 @ Cl• → >ot permici*le

Cl – CCl3

H – CCl3 → 'irst attacking fran7uent

– Cr 3

: /alogenation :

r

〉 C + C 〈 .# 02

tem' oom

CCl Br → 〉 C – C 〈

→ 5lectrophilic addition

→ Occurs through. ech, J 〉 C + C 〈

c!clic *romoaion c!clic *romination ↓ r – r

intermediate *ecame 〉 C – C 〈

it is more sta*le than C⊕ r ⊕

r

〉 C – C 〈 〉 C – C 〈 〉 C – C 〈

r () ↓ r (.) r

Complete octet of n complete octet /nti addition due to c!clicintessmer

all 3 – atoms octet of can*on.

"# -rite the pro%uct:

Cl CH3 – CH + CH2 r 2#H2O

↓ >aCl#r 2

Cl OH

CH3 – CHJ CH2 CH3 – CH – CH2 CH3 – CH – CH2 (a=)

Cl (a=) r r

CH3 – CH – CH2 – r CH3 – CH – CH2

r r

2. → 2 Br (Trans onl! oth ehantiomer)


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r CH3 H r H CH3

CH3 CH3

H r H r

i.e ehantiomers (/cti"e) es

CH3 CH3 CH3

H r r H H r

r H H r H r

CH3 CH3 CH3

/y%ration

CH3 – CH + CH2 OH

→ + O H H 2# CH3 – CH – CH3

0

22

.2

#)(.

BaBH

O H OAC Hg → CH3 – CH – CH3

OH

OH

− → OH O H

H B

#.2

.

22

62

CH3 – CH2 – CH2

(ci% catalyse hy%ration:

() CH3 – CH + CH2 → CH3 – CH – CH3

→ 5lectrophilic addition OH

→ arkohikott:s rule followed. CH3 – CH – CH3

→ C – interus. o rearrangement is possi*le. OH2

CH3 – CH – CH2

OH

(a) CH3 – CH – CH + CH2

CH3 ↓ H2O0#H2O

OH

CH3 – C – CH2 – CH3 ↓ H@ # H2O

CH3 (a=or)

@ CH3 – CH – CH – CH3

CH3 OH (inor)

→ Bia o!mercuration # demercunation.

CH3 – CH + CH2 CH3 – CH – CH3

DI

CH3

CH3

CH3 (a=)


58/60

Hg(O/C)2 ↓ o!mercuration. OH

JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ

ech, CH3 – CH + CH2 O/C

Hg

O/C

→ 5lectrophilic addition H2O

→ – "alue followed CH3 – CH – CH2

→ >o C@ − ion rearrangement. Hg

↓ O/C

OH

CH3 – C – CH2

Hg O/C.


59/60

D8

CH3 CH3


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6

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