Name Reaction Rearrangement
Transcript of Name Reaction Rearrangement
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CONTENT
1) Pinacol Rearrangement
2) Wagner-Meerwin Rearrangement
3) Beckman Rearrangement
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PINACOL
REARRANGEMENT
Pinacol are ditertiary 1,2-diols.
the simplest member of this class is Me2C(OH).C(OH)Me2.
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Wilhelm Rudolph Fittig (6 December 1835 – 19 November 1910) was a
German chemist. Fittig discovered the
pinacol coupling reaction.
R C
OH
R
C
OH
R
R
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When pinacol is treated with dilute moderately conc. H2SO4 a
rearrangement reaction takes place which leads to the formationof Me3C.CO.Mepinacolone!.
"he acid catalysed rearrangement of #ic diols $%2 diols! toketone or aldehyde with elimination of water is known as &inacolpinacolone rearrangement.
'(ample shows that the migration origin and migration terminus are the two ad)acent car*on atoms.
the migrating group may *e aryl group+ or alkyl an H atom.
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CH3 C
OH
CH3
C
OH
CH3
CH3
HCH3 C
CH3
CH3
CH3C
O
Pinacol Pinacolone
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Mechanisms:
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Step1: reversible protonation to a hydroxyl group and elimination of
water molecule
Step2: formation of non-classical carbenium ion , a bridged intermediate.
R C
OH
R
C
OH
R
R
H
R C
OH2
R
RC
R
OH
C C
R
R
R
R
OH
C C
R
R
R
R
OH
C C
R
R
R
ROH
Bridged intermediate
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Step3:actual migration of a group to form the classical carbenium ion.
Step: !he loss of proton and the formation of oxo compound.
R 3C C
R
O H
R 3C C
R
O
+ H
C C
R
R
R
ROH
Bridged intermediate
R C
OH
R
C
R
OH
R 3C C
R
O H
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STEREOCHEMISTRY:
"eaction is intra molecular.
#hen different group are present on $ atom bearing the hydroxylgroups, two %uestion arise.
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1. Which of the two OH group willbe protonated.
2. Which of the group will
migrate?
1. Which of the two OH group
will be Protonated?
2. Which of the group willmigrate?
C C
HO
Ph Me
OH
MePh
2-methyl-1,1-diphenylpropane
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Sta*ility order of the car*enium ions. ,ecreasing sta*ility order ofcar*enium ion is
-sually that &' receives the proton which produces the more sta*lecar*enium ion *y elimination of water molecule.
thus in this e(ample OH gr. On the C atom holding the phenyl gr Will
recei#e the proton since the sta*ility of diphenyl car*enium ion is greater than that OH dimethyl car*enium ion.
Sta*ility of car*enium ion depend on the delocaliation of positi#e chargeon the C atom either through resonance or through hyper con)ugation.
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Answer of
Q1
Ph2CH > Ph CMe > PhCH >(CH3)2C .CH3CH
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"here is no clear cut answer in so far as migratory preference isconcern.
/t has found that a gr in anti or trans position with respect to thelea#ing group+ H2O+ in the more sta*le conformation of the &rotonatedsu*strate migrate preferentially.
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Answer of
Q2
C C
HO
Ph Me
OH
MePh
H2SO4
C C
Ph
Ph Me
O
Me
2-methyl-1,1-diphenylpropane-1,2-diol
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Methyl shift
#agner-(eerwein rearrangement
!he #agner-(eerweinrearrangement is an organicreaction used to convert analcohol to an olefin using an
acid catalyst.
OH
HH
OH2 H
H
conc. H2SO
4
_ H
2O
_ H+
+
+
+
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(echanism
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BEKMANN REARRANGEMENT
It is
reaction
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The Beckmann rearrangement, named after
the German chemist ERNST OTTO
BECKMAN (1853–1923),
It is an acid catalyzed conversion ofketo
oximestoN substituted amidesusually calledthe Bechmann rearrangement.
C
OH
R'
R
1.PCL!ether
or H2SO4
2.H2OR C
O
"HR'
"
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OXIMES
oIn organic chemistry, compounds containing the groupingC = N-OH,
derived fromaldehyde and Ketonesby condensing them withhydroxylamine.
oTwo types of oximes are known:
Aldoxime: combination of aldehyde with hydroxylamine.
Ketoxime: Combination of Ketones with hydroxylamine.
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R2CO
NH2
OH
R2C=NOH
H+RCHO RHC=NOH
+
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MECHANISM
Step1) Formation of a better leaving group
Step2) Ionization step
migration of anti group (w.r.t.leaving group) loss of leaving group
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C
R
R'
N
OHH2SO4 C
R
R'
N
OH2
C
R
R'
N
OH2
C
R
N
OH2
R'
R.D.step
R C N R'
R C N R'
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Step3) Nucleophilic attach by water molecule to carbenium ion
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R C N R'H2O
C N R'
OH2H
R
-HC N R'
R
O H
R C
O
NHR
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GRIGNARD REACTION
François Auguste Victor Grignard (May 6,
1871 inCherbourg - December 13, 1935 inLyon)
was aNobel Prize-winning Frenchchemist.
Introduction
Formula RMgX.it is prepared by the reaction
ofmetallic magnesiumwith the appropriateorganic halide.(R=ALKYL/ARYL/ALKENYL)
halied in order of reactivity (I> Br> Cl>> F).
Anhydrous etherRX + Mg RMgX
Grignard
reagent
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Organolithium compound:
Less prone to unwantedside reaction. Lithium is more
electropositive than magnesium. Carbon lithium bond are more
polar than carbon magnesium bond. This aremore reactivethanGrignard reagent.
halide.(R=ALKYL/ARYL/ALKENYL) halide in order of reactivity
(I> Br> Cl>> F).
RX + 2Li RLi +LiX
Grignard reagent
WHY GRIGNARD SYNTHESIS IS SO IMPORTANT?
because it enable us to take two organic molecules and convert
them into bigger one.
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Anhydrous ether
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Mechanism:
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Reaction:
R#g$C O % C
R
OH % #g&OH$
(lcohol
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STEREOCHEMISTRY
the reaction of carbonyl group can establish a steriocenter.if the
reactant aresymmetric ,equal amount of the two enantiomers are
formed,
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•)* one o* the reactant are a+ymmetric, there i+ a predominance o* the
one o* the to po++ile dia+tereomer+
Ph Et
O
1#e#g)
2HPh
Et
OHMe
1Part+
%
PhEt
MeHO
1 part
Ph CHO
MeH
1#e#g)
2H
Ph
H Me
Mr
HHO
%Ph
H Me
Mr
OHH
2 P(R 1 P(R
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REACTIONS:
reactions are classified with reference to the type of
compound which is obtained. Hydrocarbons:
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/rignard reagent react ith al0yl halide+ and related compond+ in the
S"2manner.the reaction ith +atrated halide are +lo and the yield+ poor ,t
allyl and enyl halide&more reacti3e than al0yl halide'react **iciently.oAlcohol:
/rignard reagent react at the caronyl caron o* aldehyde and 0etone to gi3e
alcohol+.
$#g R % CH5 X R CH3 % #g$2
$#g R % O
R'
"R
R'
"R
R O MgX
HR'
"R
R OH
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Aldehyde:
The reaction of Grignard reagent with ethyl orto format gives
an acetal which is converted by mild acid hydrolysis into
the aldehyde
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oKetones: Three methods are available
1)from nitriles.
EtO
EtO
OEt + RMgX
EtO
EtO
OEt + RMgOEt + $
RMgX + R C NR
R
O
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2)from N-substituted amides.
3)from acid chlorides
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RMgX + O
R
N2"R
O
R'
R
+ MgX + R"2NH
C6H11#gBr 1'PhCOCl
2'H
O
PhC6H11
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Reaction at element other than carbon: Grignard reagent may be used to attach various other
element to carbon. The following type of compound can be
obtained.
1)hydro peroxide
2)Thiols
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Me3C MgX
O2Me3C O O MgX
HMg3C CO2H
RMgX + S R S MgX
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4)iodide.
5)amines
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3)sulfinic acids
RMgX + R + MgX
RMgX + NH2 OCH3 R NH2 + MgX!OCH3
RMgX + SO2 R S
O
O
MgX
H
R S
OH
O
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Limitation:
Solvent must be scrupulouslydried and freed of the alcohol from
which it was very probably made.
Grignard reagent will not even form in the presence ofwater. Apparatus must be compleltydry before start. Protect reaction
from reaction fromwater vapors.
Grignard reagent can not prepare from a compound
(HOCH2CH2Br) that containaddition halogen/some other group (-
OH) that will react with a Grignard reagent.
In preparation of aryl magnesium halidesubstituent present on
benzene ring like –COOH.-OH,-NH2,-SO3Hcontain hydrogen
attach to O or N are so acidic that theydecompose Grignard
reagent.
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