15_Aldehyde and Ketones

8/13/2019 15_Aldehyde and Ketones

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ALDEHYDES & KETONES 48

Introduction

Aldehydes are the compounds which have general formula RCHO, Ketones are compounds having

general formula RR CO. The groups R and R may be aliphatic or aromatic, similar or differentalyl!aryl groups.

"oth aldehydes and etones contain the carbonyl group, C O,= and are often referred to collectively ascarbonyl compounds.

#t is the carbonyl group that governs mainly the chemistry of aldehydes and etones.

Structure of Carbonyl Group

Carbonyl carbon is $oined to three other atoms by bonds% since these bonds utili&e 'sp orbitals, they lie

in a plane, and are (')* apart. The remaining p+orbitals of carbon overlaps a p+orbital of oygen to form a bond% carbon and oygen are thus $oined by a double bond. The part of the molecule immediatelysurrounding carbonyl carbon lie in a plane.

The electrons of a carbonyl double bond hold together atoms of -uite different electronegativity and

hence the electrons are not e-ually shared% in particular the polar + cloud is pulled strongly towards the

more electronegative atom, oygen.The carbonyl group, C O,= governs the chemistry of aldehydes and etones. #t does this in two ways

/a0 "y providing a site for nucleophilic addition, and

LDEHYDES & KETONESLESSON15

C O=

H

RAn aldehyde

C O=R

R

A etone

C O=R

R

+

(')

R

RC O=

1


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/b0 "y increasing the acidity of hydrogen atoms attached to the alpha carbon.

Physical Properties

The polar carbonyl group maes aldehydes and etones as polar compounds and hence they have higher

boiling points than non+polar compounds of comparable 2.3. "y themselves they are not capable of

intermolecular hydrogen bonding since they contain hydrogen bonded only to carbon% as a result they

have lower boiling points than comparable alcohols or carboylic acids.

For example

The lower aldehydes and etones are appreciably soluble in water, because of hydrogen bonding between

solute and solvent molecules% borderline solubility is reached at about 4 carbons. Aldehydes and etones

are soluble in the usual organic solvents. 5ormaldehyde is a gas /b.p 6 '(*0 and is handled either as an

a-ueous solution /5ormation0, or as one of its solid polymer paraformaldehyde ( )' nCH O , or trioane,

( )' 7CH O .

Acetaldehyde /b.p. ')*0 is often generated from its higher+boiling trimer by heating the trimer with acid.

H8

R C C R

8 88H O

7

sp '

sp

Compare n+butyraldehyde

methyl ethyl etone

( )b.p. 9:*

( )b.p. ;)*

n+butyl alcohol

propionic acid

( )b.p. ((;*

( )b.p. (


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' '

=.C.C.

' CH ClRCH OH R CHO

CPP

(. 3hich of the following etones is more acidic and why>

Preparation

A few of the many laboratory methods of preparation of aldehydes and etones are outlined below% /most

of these are already familiar to us0 #ndustrial preparation is generally patterned after these laboratorymethods, but with use of cheaper reagents alcohols are oidi&ed catalytically with air, or by

dehydrogenation over hot copper.

Preparation of Aldehydes

Oxidation of primary alcohols

/"y special distillation method0

/=yridinium chloro+chromate0 /=.C.C.0

Example :

' ' 9 '


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7 ' ' 7 7 ' ' 7CH CH CH CHCH CH CH CH COCH8OH

Example :

Reduction of acid chlorides

Reimer-Tiemann Reaction-Phenolic Aldehydes

/iscussed under phenol0

By heating a mixture of the calcium salts of formic acid and any one of its homologues.

Stephens !ethod

'H O /Hydrolysis of intermediate0 RCH @H= to RCHO and 7@H

Preparation of Ketones

Oxidation of Secondary alcohols

CPP

'. ?uggest the suitable reagents for the following conversions.

/a0 7 ' ' ' ' 7 ' ' 'CH CH CH CH CH OH CH CH CH CH CHO

/b0

/c0 7 ' ' 7 'CH CH CH CHCH OH CH CH CH CHCHO= =

7CH

p+"romotoluene

"r 'CHCl"r'Cl , heat

light CHO"r7 '

CaCO , H O

p+"romoben&aldehyde

7CH

p+nitrotoluene

'O @ ( ) 'CH OAc'O @ 7

'

CrO

Ac O CHO'O @

'

'

'

O O88 8 88 8C C C C H

8 8H

+ +

' ' ' ' Cl , "r , #=

4O =Cl== + Cl

7=OCl+Cl

O88


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?ubstrate aldehyde or etone containing hydrogen

Reagent ( )

dilute base

commonly used , =roduct + hydroaldehyde or + hydroyetone

Mnder the influence of dilute base or dilute acid, two molecules of an aldehyde or etone may combine to

form a + hydroyl aldehyde or etone.

The + carbonion generated by the base from one molecule of aldehyde. Or etone adds to the carbonylcarbon of the other molecule and the two molecules condense and form + hydroyl aldehyde or etone.et us consider the mechanism for the OH catalysed aldol condensation of acetaldehyde

Aldol condensations are reversible, and with etones the e-uilibrium is unfavourable for condensation

product. + hydroycarbonyl compounds are readily dehydrated to give + + unsaturated carbonylcompounds. 3ith Ar on + carbon, only dehydrated product is isolated.

An aldol condensation between two different carbonyl compounds so called crossed aldol condensation 6

is not always useful as a miture of four different possible products may be obtained.

' '

H8

HO H C CHO CH CHO H O8H

+ +

7 ' 7 'CH C CH CHO CH CH CH CHO

88 8O O

+

'H C CH O=

Key step in condensationH

7 ' 7 'CH CH CH CHO H O H CH CH CH CHO8 8O OH

+

+hydroyaldehyde

Aldol Condensation

Crossed Aldol Condensation


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Mnder certain condition, a good yield of a single product can be obtained from a crossed aldol

condensation. One reactant contains no + hydrogens and therefore is incapable of condensation withitself /e.g. Aromatic aldehydes or formaldehyde0.

CPP

((. ?how how each of the following compounds may be prepared from simple aldehydes or etones

utili&ing aldol reaction.

/a0 /b0

/c0 /d0

('.

/a0 /b0

OH

H8

C O

=

Cinnamaldehyde

7CH CHO,')

7 7CH COCH

())

4: 7C H COCH

H H H8 8 8

C C C O = =

7

H H O8 8 88

C C C CH =

H H8 8

C C C88O

=

Crossed AldolCondensations

O88

CHO

CHO

OH

O88

OH8


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H H8 8

Ar C O OH Ar C O

8OH

= +

'

O88

=h I CH CH I CH I C I H==

7 ' '

O88

CH CH CH CH I CH I C I H==

7

O88

=h I CH C I C I H8CH

==

/c0 /d0 @one of these.

(7. 5ind the ma$or product of given reaction

/a0 /b0 7 '

7

O88

CH CH I CH C I C I H8

CH

==

/c0 /d0

Reactions Related to the Aldol Condensation

iscussion #n the presence of concentrated alali, aldehydes containing no + +hydrogens undergo self+oidation and reduction to yield a miture of an alcohol and a salt of a carboylic acid. This reaction is

nown as Canni,,aro - reaction.

Two successive additions are involved.

/a0 Addition by hydroide ion in first step

/b0 Addition of hydride ion in the net step

H O H O8 8 8 88

Ar C O H C Ar Ar C H HO C Ar 8 8OH O

= + +

H O8 88

Ar C H O C Ar 8OH

+

r.d.s. /=roton echange0

Canni,,aro Reaction


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OH8

R C O OH R C O8 8H H

= +

This eplains the Crossed Canni&&aro reaction involving formaldehyde to tae place in the way that

it does.

' 'ArCHO HCHO HCO @a ArCH OH++ +

On both electronic and steric grounds, the step ( is faster for HCHO. Hence becomes the hydride

donor in the net step.

Illustration /i0 #n the presence of concentrated OH ,

aldehydes lacing an + hydrogen undergo theCanni&&aro reaction. Nive the products of the reactions of /a0 ben&aldehyde

/b0 trimethylacetaldehyde /c0 furaldehyde.

/ii0 /a0 ?uggest a mechanism for the Canni&&aro reaction. abel the slow step.

/b0 How does the mechanism account for the fact that the product alcohol contains no

carbon+bound deuterium when the reaction is run is ' O>

Solution /i0 /a0 '=hCH OH =hCOO+ /b0 7 ' 72e CCH OH 2e CCOO+

/c0

/ii0 /a0

/b0

#n /b0 that was originally the aldehydic H is transferred /hydride transfer directly from the

adduct anion to a second aldehyde molecule without any instrusion by solvent ( )' O .

H H8 8

H C O OH H C OH8O

= +

' '

H H8 8

Ar C O H C OH ArCH OH HCO8O

= + +

O

'CH OH +O

COO

slow'

OH H OH8 8 8

IIR C O R C O R C O R C O RCOO R CH OH + = = + +

H

HH


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CPP

(

/ii0 3hy is 'H CO always oidi&ed in the crossed+Canni&&aro reactions in previous

problem>

/iii0 Nive the products of the Canni&&aro reaction of =hCOCHO /A0 and '=hCOCHCl /"0 and

eplain their formation

Gster can be condensed with aromatic aldehydes in the presence of aloides% thus ben&aldehyde and

ethylacetate in the presence of sodium ethoide, give ethyl cinnamate, : 4 ' 4C H CH CHCOOC H .=

)aloenation of Ketones

OGt

7

H8

C O CH C OGt88O

= + CH CH C = O

OGt

' ' '

H OH8 8=h C O CH C O Gt =h C CH CO Gt =h CH CH CO Gt

88 8 8O H H

= + =

H or O H

'C C %8 88H O

+

+ ' ' ' 'C C H Cl , "r , #8 88 O

+ =

Ketone /a Halo Ketone0

( ) 7CH COO@a7 : 4 ''CHO CH CO O C H CH CH CO H + =Acetic Anhydride Cinnamic acid

7

H8

=h C O CH C = +

7H C C

O

O

O

hydrolysis

H H8 8

=h C C C =

O

OH

7+=henylpropenoic acid

OAc

A Per#in Condensation


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Examples :

*ote :

The Haloform Test depends upon the fact that the three hydrogens on the same carbon atom are

successively replaced by halogen. Taing acetone as an eample we see that the carbon that suffers theinitial substitution to the preferred site undergoes further substitution.

Glectron withdrawal by halogen maes hydrogens on the carbon to which halogen has already being

attached more acidic and hence more readily removed by base to give further substitution.

Glectron withdrawal by three halogens maes 7C

comparatively wealy basic /for a carbanion0 and

hence acts as a good leaving group.

Thus both essential aspects of the haloform reaction 6 regiospecificity of halogenation, and cleavage 6 are

controlled by the factor% stabili&ation of a carbanion through electron withdrawal.

OH

'"r

+

+

O

"rH"r+

7 7

OH

7 7 ' 7 7

7 7

CH CH8 8

CH C C CH # OH CH C C C#8 88 8 88CH O CH O

+ +

7

7 ' 7

7

CH8

CH C CO CH#8CH

+

H 8 8

H C C C H8 88 8H O H

7

8

H C C C H88O

OH

H 8 8

H C C C H

88 8O H

7

8C HH C C

8O

=

X @ot formed

7R C C88O

OH

7

OH8

R C C8O

7

OH8

R C C88O

+ ' 7R CO HC

+

Claisen Condensation/ Formation of 0 1 Keto Esters


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Ketones /but not aldehydes0 undergo a crossed Claisen Condensation with ester.

Example :

!ecarboxylation of 0 1 Keto Acids

+ Keto esters are normally prepared by Claisen Condensation. Hydrolysis of the + eto ester gives the+ eto acids which are very easy to decarboylate simply by heating. ecarboylation of free acetoacetic

acid involves transfer of the acidic hydrogen to the eto+group followed by loss of carbon+dioide via a

cyclic :+membered T.?.

Addition of Ammonia

Aldehydes react with ammonia to form aldehyde ammonia

The aldehyde ammonia is unstable and lose water immediately to form aldimine. The dehydration product

is not usually obtained because, in most cases, it immediately polymerises to form cyclic trimers.

' 4@aOC H

7 ' 4 7 7 7 ' 7 ' 4CH COOC H CH COCH CH COCH COCH C H OH+ +Gthyl acetate Acetone Acetylacetone

Aldehyde ammonia

7C O @H= + R

C

H

R

H

OH

'@H

' 'D

(. H O OH(. @aOGt

7 ' 7 ' ' 7 ' ''. H '. H'CH CO Gt CH C CH CO Gt CH C CH CO H

88 88

O O

+

/ecarboylation0

O88 'CO

'CO H

O88

7 7 'CH COCH CO +

7 ' 'CH C CH CO8OH

= +

7 7CH C CH88O

7CH C88O

C O8O

=

'CH

H


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3hen treated with ammonia, formaldehyde does not form an aldehyde 6 ammonia, but gives instead

heamethylenetetramine, used in medicine as a urinary antiseptic under the name Mrotoropine.

Ketones also give etone+ammonia but these cannot be isolated. Acetone reacts slowly with ammonia to

form acetone ammonia and then a comple compound.

Acetone upon treatment with ammonia at higher temperature give acetoneammonia.

Aldimines, ?chiffLs bases or a&omethines are formed when aldehydes react with aliphatic primary amines,

which is removed by slow distillation.

Aldehyde ammonia/unstable0

7C O @H= + 7CH

C

H

7CH

H

OH

'@H

'H O C @H=7CH

H

Aldimine /very reactive0

7C @H @H polymerisation= + 7CH

H

( )7 ' < '::HCHO


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The carbonyl compound is heated with aluminium isopropoide in isopropanol solution, the isopropoide

is oidised to acetone, which is removed by slow distillation.

The reducing agent is specific for the carbonyl group, and so may be used for reducing aldehydes and

etones containing some other functional group that is reducible e.g., a double bond or a nitro group.

/(, '+methyl but 6 (, ' diol0 upon treatment with hot dil. '


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Formaldehyde/ 2ethanal/ )1C)6&

Preparation

(. "y the reduction of carbon monoide 5ormaldehyde is produced from carbon+monoide when a

miture of these gases /water gas0 is passed at low pressure through an electric discharge of low

intensity.

'. "y oidation of methyl alcohol+large -uantities of formaldehyde are prepared by passing a miture

of methyl alcohol vapour and air over heated copper or silver.

A catalyst composed of molybdenum trioide and ferric oide Converts 4 of methyl alcohol to

formaldehyde. #n the oidation method, the condensate obtained is a miture of formaldehyde,methanol and water. #t is freed from ecess of methanol by distillation, and the resulting miture is

nown as formalin/


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7CH

8CH

7

O8

H C CH7

O8CH CH

O

( )#

' ' '

('CuCl 'HCl O 'CuCl H O

'+ + +

' ''CuCl =d 'CuCl =dCl+ +

' ' ' ' 7CH CH =dCl H O CH CHO =d 'HCl= + + + +

Ag air

7 ' 7 ' 7 'AgCH CHO H CH CH OH CH CHO H O+ +

5ormaldehyde can participate in a crossed Canni&&aro reaction.

: 4 : 4 ' 'C H CHO HCHO @aOH C H CH OH HCO @a+ + +

Aldehydes with one + hydrogen atom reacts as follow

?imilarly,

Acetaldehyde/ $Ethanal% =7C) C) &

Acetaldehyde /ethanal0 is prepared industrially

/i0 "y the dehydrogenation or air oidation of ethanol in the presence of silver catalyst at 7))*C.

/ii0 "y passing a miture of ethylene and oygen, under pressure, into an a-ueous solution of =d and

cupric chlorides at 4)*C.

Acetaldehyde is a colourless, pungent smelling li-uid, b.p, '(*C.

Polymers of Acetaldehyde

3hen acetaldehyde is treated with a few drops of conc. '


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alcoholate which separates out as a crystalline solid. This on distillation with concentrated '


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/ii0 #t does not readily polymerise e.g. it does not resinify with @aOH, but undergoes canni&&aro

reaction.

"en&aldehyde may be prepared by any of the following methods, which are general for its

homologues as well.

(. "y hydrolysis of ben&ilidene chloride with a-ueous acid /this is also a commercial method0.

: 4 ' ' : 4C H CHCl H O C H CHO 'HCl+ +

'. "en&aldehyde may be conveniently prepared in the laboratory by oidising toluene with 7CrO in

acetic anhydride.

As the ben&aldehyde is formed, it is converted into ben&ilidene acetate, thereby preventing further

oidation of the ben&aldehye. Hydrolysis of the acetate with dilute sulphuric acid or hydrochloric

acid gives ben&aldehyde.

( ) ( )7

7 '

CrO H

: 4 7 : 4 7 : 4 7 'CH CO O 'C H CH C H CH OCOCH C H CHO 'CH CO H

+

+

A better yield of ben&aldehyde may be obtained by oidising ben&yl alcohol with 7CrO in acetic

anhydride.

An interesting oidising agent is chromyl chloride $Etard9s reaction%. #n this method toluene is

treated with chromyl chloride in


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3hen ben&ene is treated with a miture of HC@ and HCl in the presence of 7AlCl , and then comple so

produced decomposed with water, ben&aldehyde is produced.

7 'AlCl H O

: : : 4 : 4 7C H HC@ HCl C H CH @H HCl C H CHO @H+ + = +

"en&aldehyde is produced when ben&yl chloride is reflued with heamethylenetramine in a-ueous

ethanolic solution followed by acidification and steam distillation.

( ): 4 ' ' < : 4:C H CH Cl CH @ C H CHO+

3hen reflued with a-ueous ethanolic potassium cyanide ben&aldehyde forms ben,oin.

Aldehydes and etones are characteri&ed through the addition to the carbonyl group of nucleophilic

reagents, especially derivatives of ammonia. All aldehyde or etone will, for eample react with

',


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Aldehydes are also, of course, oidi&ed by many other oidi&ing agents by cold, dilute, neutral


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/c0 /d0

(:.

#dentify name of reaction

/a0 Aldol condensation /b0 Canni&&aro condensation

/c0 Crossed Claisen condensation /d0 Tischeno Reaction.

(9.

/a0 /b0

/c0 /d0


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( )( )

7 '

Optically active

CH CH CH OH COOH ( )( )

7 '

Optically active

CH CH COOH CH OH

( )'

7

H Oa- KOH

7 ' 7 ' 7 '

7

CH8

'CH CH CHO CH CH CH CH CHO CH CH CH C CHO8 8OH CH

=

(

This etone is more acidic because the resulting enolate ion obeys HucelLs rule and thus

more stable.

' /a0 Cu or CuO,

/b0 ' ' 9K Cr O , H+

/c0 =.C.C. or 'Ag O

7 /A0 /"0

/C0 : 4 ' ' : 4C H CH CH C CC H


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/c0

/d0

Totally convert any of the aldehydes to the carbanion by using strong base, followed by

reaction with the other aldehyde. This is done to avoid multiple products.

('. A

(7.

(


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Problem A etone A which undergoes a haloform reaction gives compound " on reduction. " on

heating with sulphuric acid gives compound C, which forms mono+o&onide . Thecompound on hydrolysis in presence of &inc dust gives only acetaldehyde. #dentify A, "

and C. 3rite down the reactions involved.

Solution 3e are given that

reductionA "

'


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formula 7 :C H O 0. G does not give TollenLs test and does not reduce 5ehlingLs solution but

forms a ',


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Solution The reaction of ' mol of an ester giving + eto ester and alcohol in the presence ofsodium ethoide is nown as Claisen condensation.

et the given reactions may be depicted as shown in the following.

5rom these reactions, it is obvious that

' 7R CH CH

7R CH

Hence, the compounds A, " and C are

Problem ; An organic compound ( ): ()A C H on reduction first gives ( ): ('" C H and finally( ): (


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that the o&onolysis product include two molecules of ( )7 CH CHO and one molecule ofG/OHC CHO0. 5rom this, we derive the structure of A as shown in the following.

The structure of " and C are as follows.

The structure of 5 is as follows.

Problem < An organic compound ( ): ('A C H O forms an oime but does not reduce TollenLs reagent.A on reduction with sodium+amalgam forms an alcohol " which on dehydration forms

chiefly a single alene C. The o&onolysis of C produces and G. The compound

reduces Tollens reagent but does not answer iodoform test. 3hat are the structures of the

above compounds> Gplain the reactions.

Solution The compound A must be a etone as it forms oime but does not reduce TollenLs reagent.

The compound must be an aldehyde. #ts structure does not include the fragmentas it does not answer iodoform test.

The compound G must be a etone containing fragment.

et the compounds and G be 'RCH CHO and R COR , respectively, where R, R andR are all alyl groups. 5rom these, we get

?ince the molecular formula of A is : ('C H O, it follows that 7R R R CH . = = = Hence,the structures of molecules /A0 to /G0 and the reactions are as follows.

( ) ( ) ( )( )

7O

7 7 7 7 G ',


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Problem = A compound A reduces 5ehlingLs solution and gives positive silver mirror test. On

warming with dilute alali, followed by dehydration it gives a product " which also

responds to both the above tests. #n addition, it decolourises the colour of bromine water.

On treatment with hydrogen in the presence of nicel under pressure the compound " isconverted to C which does not give any one of the above three test. 2olar mass of the

compound C is(9< g mol . educe the structures of A and " giving the chemical

e-uations involved.

Solution The compound A must be an aldehyde as it reduces 5ehlingLs solution and gives positive

silver mirror test. The compound A also contains + hydrogen atom as it undergoes aldolcondensation, the dehydration of which gives ". The latter contains unsaturation as

bromine water is decolourised. et the structure of A be 'RCH CHO. The reactions

involved are

The reduction of " with 'H ! @i under pressure would be

?ince the molar mass of C is(9< g mol , R in the compound C must be hydrogen atom.

Hence, the structures of A, " and C are.

A 7CH CHO " 7CH CH CHCHO= C 7 ' ' 'CH CH CH CH OH

7 'CH CH CCH88O

7CH

/A0

7CH

[ ]H7 'CH CH CHCH

8OH

7CH

7CH

/"0

5orms oime but does not reduce

Tollens reagent

alcohol

7O

7 ' 7 7 7 'CH CH CHO CH COCH CH CH CH C+ =7CH

7CH/0 /G0 /C0

Reduce Tollens reagent

but no iodoform test

oes not reduce Tollens reagent

but gives iodoform test

'H O

@aOH' 'RCH CHO H CCHO

8R

+ 'RCH CH CH CHO8 8OH R

'RCH CH C CHO8R

=

'H O

/"0

'H ! @ i

'RCH CH CCHO8R

=

( )

' ' '

C

RCH CH CHCH OH8R


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CHO

'CH OH

H OH

Problem > 3hen R glyceraldehydes, ( )'CH OHCH OH CHO is treated withcyanide and the resulting product is hydrolysed, two monocarboylic

acids are formed. These acids are identical with the acids obtained by

oidation with '"r + water of ( ) threose and ( ) erythrose. Assign

single structure to ( ) erythrose and to ( ) threose.

Solution

@ote The erythro isomer is the one that is convertible /in principle at least0 into a meso

structure, whereas the threo isomer is convertible into a racemic modification. The names

of these compounds are the basis for designations erythro and threo acid to specify certain

configuration of compounds containing two chiral carbons.

Problem ? How starting from /# and ##0, one can get /###0,


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( )@aOH,

aldolO A==

===

O88

=== O===

===

O==

O 88 8 C O , C OH

8

O 88 8

C O , C OH8H

O 88 8

O C O , C OH8

Problem

/a0 /b0

/c0 /d0

Solution a

H at C taes part which is condensed to carbonyl group of second molecule% heatingcauses , elimination.

/a0Problem (

Canni&&aro

''C O OH= + and P /P is alcohol, is deuterium0 and P will have

structure

/a0 /b0

/c0 /d0 none is correct

Solution c

SOLVED OB ECTIVE PROBLEMS

8 8 C O OH O C

8OH

= + + C O O C= =

8 C O

8

+

OH

O C=

O

8

C OH8

+

=rotontransfer


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7

O88

CH C COOH ( )' 'CH COOH

7

O88

CH C CHO '

O88

H C CH COOH

7CH CH CH 2g"r CH C 2g"r +

( )COOH is G3N CH C COOH

'OHC CH COOH

'HOOC CH COOH

'Ag O

< '


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'?eO

7 7

O88

CH C CH A

'

'

'

CH OH8

HOH C C CHO8CH

Problem >

A will

/a0 reduce Tollens reagent /b0 give iodoform test

/c0 form dioime /d0 give Canni&aro reaction

Solution a/ b/ c and d

'?eO oidises 'CH w.r.t. eto group

/a0, /b0, /c0 and /d0Problem ?

@aOH

77HCHO CH CHO A. A+ can

/a0 reduce TollenLs reagent /b0 give Canni&&aro reaction

/c0 react with @a /d0 give green colour with

'

' 9Cr O ! H

+

Solution a/ b/ c and d

A is by aldol condensation

/a0, /b0, /c0 and /d0Problem 3hen aldehyde is heated with 5ehlingLs solution, it gives a precipitate of

/a0 Cu /b0 CuO

/c0 'Cu O /d0 'Cu Cu O CuO+ +

Solution c

Copper ?ulphate is reduced to 'Cu O

/c0Problem @ Aldol condensation is not given by

/a0 7CH CHO /b0 7 7CH COCH /c0 7 'CH CH CHO /d0 HCHO

Solution d

5ormaldehyde does not have alpha hydrogen atom

/d0Problem 3hich of the following gives positive iodoform test and positive 5ehilingLs solution test>

/a0 acetone /b0 acetaldehyde /c0 ethanol /d0 formaldehyde

Solution b


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Acetaldehyde has 7CH CO group as well as CHO group.

/b0Problem ( The best oidising agent for oidation of 7CH CH CHCHO= to 7CH CH CH COOH= is

/a0 acidified

/a0dil. @aOH

7 7 ''CH CHO CH CHOHCH CHO

/b0 ( ) ( )dil. @aOH7 7 7 7 ' 7'CH COCH CH C OH CH CH COCH

/c0dil. @aOH

7'HCHO CH OH

/d0dil. @aOH

: 4 : 4 'C H CHO HCHO C H CH OH+

Solution a/ b

Aldol condensation is the condensation of carbonyl having + hydrogen

/a0, /b0


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C8SE PR&8BE2S

(. Nive the #M=AC name of

'. An organic compound with molecular formula, ()C H O forms ',


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'O @ ( ) ( ) ( )7 'CH CH COO@a

7 ' Heat'CHO CH CH CO O +

CH CH COOH = 'O @ CH CH COOH =

7

CH C COOH8CH

= 'O @

AIP25AIEEE1SI*GBE C)&ICE C&RREC5

(.

#dentify final product Q1L

/a0 CH#7 /b0 HC CH /c0 /d0 H'C CH'

'. 3hich one of the following reagent is used to convert acetone into ',76dimethylbutane6',76diol>

/a0 '2g Hg ! H O /b0 1n Hg ! HCl /c0 @a Hg ! @aOH /d0 All of these

7. #dentify the product /0 in the following reaction.

/a0 /b0

/c0 /d0

( )H7 'CH CHO @H OH =+

+

/a0 7CH CH @ OH = /b0 Only syn aldoime/c0 Only anti aldoime /d0 @o product will be formed

4. Consider the following se-uence of reaction

The product " is

/a0 /b0 /c0 /d0

EXERCISE II

7CH CH C COOH8

=

'

8@O


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'H O== O==

( )< '@a"H ! H O A

( )

( ) ( )' :

' '

i " H

ii H O !OH "

'CH == OH and 'HOCH O==

7CH O== and 'HOCH O==

'

CH == and'

HOCH O==

( )Conc. @aOHO O88 88

=h C C H

' '

O

88H @ C @H && && ' : 4 'p @O C H @H &&

'

O88

H C @H && : 4 'C H @H@H&& &&

:.

The compounds /A0 and /"0 respectively are

/a0

/b0

/c0

/d0

9. The order of reactivity of the following compounds with : 4C H 2g"r is

/#0 : 4 : 4C H COC H /##0 7CH CHO /###0 7 7CH COCH

/a0 ( ) ( ) ( )# ## ###> > /b0 ( ) ( ) ( )### # ##> > /c0 ( ) ( ) ( )## # ###> > /d0 ( ) ( ) ( )## ### #> >

;. #dentify the product /0 in the following reaction

/a0 '=hCOCO H /b0 ( ) '=hCH OH CO @a

/c0 ( ) '=h CH OH CH OH /d0 '=h CH CH =

. Among the following compounds, which will react with acetone to give a product containing

/a0 /b0

/c0 /d0

(). #n the Canni&&aro reaction given below,OH

' ''=h CHO =h CH OH =hCO +

the slowest step is

7CH OH and 7CH

O==HO

C @ >=


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7 7

O88

CH C CH 7 ' 7

O O88 88

CH C CH C CH

7 ' 7

O O88 88

CH C CH C OCH 7 ' 7

O O88 88

CH C CH C ? CH &&&&

O==@H

O==@H

O==@H

/a0 the attac of OH at the carbonyl group

/b0 the transfer of hydride ion to the carbonyl group

/c0 the abstraction of proton from the carboylic acid

/d0 the deprotonation of '=h CH OH

((. Hydrolysis of an ester gives acid /A0 and alcohol /"0. #f compound /"0 is ' 4C H OH and molecular

formula of ester is < ; 'C H O , then ester will be

/a0 2ethyl formate /b0 Gthyl formate /c0 2ethyl acetate /d0 Gthyl acetate

('. ?chiffLs reagent is prepared by discharging the pin colour of the dye

/a0 methyl orange /b0 pararosaniline hydrochloride

/c0 rosaniline hydrochloride /d0 phenolphthalein

(7.

The value of e-uilibrium constant will be highest for

/a0 HCHO /b0 7CH CHO /c0 7CCl CHO /d0 : 4C H CHO(


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: 4

: 4 '

C H8

C H CH CH C CHO=

: 4 '

: 4

C H CH CH CH CHO8 8OH C H

: 4 ' ' 'C H CH CH CH CO H8OH

7 7

O88

2e C C CH 7 ' 4

O88

2e C C C H

7 7

O88

2e C C C2e 7 '

O88

2e C C CH2e

(;. #n the reaction,( )

( ) ( ) ( )' : ' ' 9 '

/a0 /b0

/c0 /d0

'


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( ) ( ) ( ) ( )7 7 7 7 ' 7CH CH CH CHO CH CO CH CH CO CH CO CH

# ## ### #S

7=h C @HCH88O

=h C @H=h88O

( ) ( )' ' ( ) ( ) ( )

( )

/a0 /b0 : 4 ' ' ' 4C H CH CH COOC H

/c0 /d0

(7. 3hat will be the product /10 formed in the following reaction>

/a0 /b0 /c0 /d0

CH CH8 8

== 'CH C

8 8

O

'CH CH8 8

OH

C C8 8

OO

O88

( ) ( )' 4C H O@a 1n!HgHeat conc. HCl

A " . 88O O

88

O

( )

( ) ( )i @aOH

ii HCl 1

O

COOH

OH

COOH

OH

COOH

OHCOOH

8OH


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( ) ( ) ( ) ( )' : < : 4 7p @O C H CHO, =h CO =h, C H CHO, CH CHO

# ## ### #S

'CH OH

O88

'

OH8CH CH OH

'CH OH

( ) ( )77

CH 2g"r ecess

H OO .+==

O

O

(

/a0 5ormaldehyde and acetone /b0 5ormaldehyde and acetaldehyde

/c0 Two molecules of acetaldehyde /d0 Two molecules of acetone

(4. An organic compound on treatment with

/a0 #t is a crossed aldol condensation reaction

/b0 The reaction yields one more condensation product besides /0

/c0 Compound /0 is

/d0 Compound /0 is commonly nown as cinnamaldehyde

(9. Arrange the following compounds in decreasing e-K Ls for cyanohydrin formation.

/a0 ( ) ( ) ( ) ( )#S ### # ##> > > /b0 ( ) ( ) ( ) ( )### # ## #S> > >

/c0 ( ) ( ) ( ) ( )#S # ### ##> > > /d0 ( ) ( ) ( ) ( )## # ### #S> > >

(;. 3hat is /0>

/a0 /b0

/c0 /d0

(. The final product of the following se-uence of reaction is

( ) 7' H OH C O2g7 ' ' ' heat'CH O CHCH CH CH "r >+=

( )dil. @aOH7CHO CH CHO +

' 'CH CH CHO

'CH OHOH

OHO

7CH

OH OH7CH

7CH

HO

OH7CH


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7 ' ' ' '

O88

CH O C CH CH CH CH OH 7 ' ' ' '

O88

CH C CH CH CH CH OH

' ' ' '

O

88H C CH CH CH CH OH ' ' '

O O

88 88H C CH CH CH C H

7 '

7

CH C @@HCO@H8CH

=

7 '

7

CH C @CO@H@H

8CH

=

( )7 'CH C # CH Cl8OK

/a0 /b0

/c0 /d0

'). Compound QAL /molecular formula 7 ;C H O 0 is treated with acidified potassium dichromate to form

a product Q"L /molecular formula 7 :C H O 0. Q"L forms a shining silver mirror on warming with

ammoniacal silver nitrate. Q"L when treated with an a-ueous solution of ' 'H @CO@H@H .HCl and

sodium acetate gives a product QCL. #dentify the structure of QCL.

/a0 7 ' 'CH CH CH @@HCO@H= /b0

/c0 /d0 7 ' 'CH CH CH @CO@H@H=

'(. 3hen a miture of 7 ' 'CH CH CH Cl and 7 'CH COCH Cl is treated with K# in acetone, then

/a0 the products are 7 ' 'CH CH CH # and

/b0 7 'CH COCH Cl reacts faster than 7 ' 'CH CH CH Cl /both by @? ' reaction0

/c0 7 ' 'CH CH CH Cl reacts faster than 7 'CH COCH Cl /both by @? ' reaction0

/d0 both under goes reaction at the same rate as both are (* halides.

''. 3hich of the following compound undergoes ready decarboylation on warming>

/a0 '=hCOCO H /b0 ' ' '=hCOCH CH CO H

/c0 ( ) ' '=hCH OH CH CO H /d0 ' ' 'HO CCH CO H

'7.'

/a0 '5CH CHO /b0 'ClCH CHO /c0 '"rCH CHO /d0 '#CH CHO

'. Carbonyl compounds show nucleophilic addition reaction with

/a0 HC@ /b0 7@aH?O /c0 7CH 2gCl /d0 All of these

7. 3hich among the following isomeric compounds is most reactive towards nucleophilic attac>

/a0 /b0

/c0 /d0 All are e-ually reactive

/a0 7 7CH COCH /b0 7 'CH CH CHO /c0 7CH CHO /d0 HCHO

4. 3hich of the following reaction does not involve nucleophilic attac on the group>

/a0 Canni&&aro reaction /b0 Aldol addition

/c0 RosenmundLs reduction /d0 Reduction by


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( )

( )7

D'

i CH 2g"r

7 7 7 7ii H ! H O

7

OH8

CH COCH CH C CH8CH

' '@H @H C @H88O

&& && &&/(0 /'0 /70

A*SERS

C8SE PR&8BE2S

(. /i0 "en&ene6(,


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. /i0 Acetophenone ( )7=hCOCH will give positive iodoform test while ben&ophenone ( )=hCO=h will not give.

/ii0 =ropanal gives positive TollenLs or 5ehlingLs test while diethyl ether does not give this test.

(). /a0 7 ' 'CH CH CH CHO

/b0 7 ' 7CH COCH CH


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AIP25AIEEE1SI*GBE C)&ICE C&RREC5

(. /b0 '. /a0 7. /d0


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2A5C) 5)E F&BB&I*G

(. ( ) ( ) ( ) ( )# C % ## " % ### A % #S

'. ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )# A , C , % ## " , C % ### " , C , % #S " , C

7. ( ) ( ) ( ) ( )# " % ## G % ### % #S C

ASSER5I&* A*! REAS&* 5PE

(. /c0 '. /a0 7. /d0

15_Aldehyde and Ketones

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Transcript of 15_Aldehyde and Ketones