name reaction rearrangement

8/20/2019 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.

2

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:

4

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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5

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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10


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11


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12


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13


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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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name reaction rearrangement

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