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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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ALDEHYDES & KETONES 49
/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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ALDEHYDES & KETONES 50
' '
=.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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ALDEHYDES & KETONES 51
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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ALDEHYDES & KETONES 63
?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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ALDEHYDES & KETONES 64
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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ALDEHYDES & KETONES 65
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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ALDEHYDES & KETONES 66
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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ALDEHYDES & KETONES 67
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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ALDEHYDES & KETONES 68
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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ALDEHYDES & KETONES 70
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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ALDEHYDES & KETONES 71
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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ALDEHYDES & KETONES 72
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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ALDEHYDES & KETONES 73
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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ALDEHYDES & KETONES 74
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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ALDEHYDES & KETONES 75
alcoholate which separates out as a crystalline solid. This on distillation with concentrated '
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ALDEHYDES & KETONES 76
/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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ALDEHYDES & KETONES 77
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 & KETONES 78
Aldehydes are also, of course, oidi&ed by many other oidi&ing agents by cold, dilute, neutral
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ALDEHYDES & KETONES 79
/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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ALDEHYDES & KETONES 80
( )( )
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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ALDEHYDES & KETONES 81
/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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ALDEHYDES & KETONES 82
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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ALDEHYDES & KETONES 83
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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ALDEHYDES & KETONES 84
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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ALDEHYDES & KETONES 85
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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ALDEHYDES & KETONES 86
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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ALDEHYDES & KETONES 87
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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ALDEHYDES & KETONES 89
( )@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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ALDEHYDES & KETONES 91
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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ALDEHYDES & KETONES 92
'?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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ALDEHYDES & KETONES 93
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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ALDEHYDES & KETONES 94
C8SE PR&8BE2S
(. Nive the #M=AC name of
'. An organic compound with molecular formula, ()C H O forms ',
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ALDEHYDES & KETONES 95
'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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ALDEHYDES & KETONES 96
'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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ALDEHYDES & KETONES 97
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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ALDEHYDES & KETONES 98
: 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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ALDEHYDES & KETONES 99
( ) ( ) ( ) ( )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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ALDEHYDES & KETONES 102
( ) ( ) ( ) ( )' : < : 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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ALDEHYDES & KETONES 103
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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ALDEHYDES & KETONES 110
( )
( )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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ALDEHYDES & KETONES 111
. /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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ALDEHYDES & KETONES 112
AIP25AIEEE1SI*GBE C)&ICE C&RREC5
(. /b0 '. /a0 7. /d0
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ALDEHYDES & KETONES 113
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