forms
an orange red precipitate with 2, 4-DNP reagent and gives yellow precipitate on
heating with iodine in the presence of sodium hydroxide. It neither reduces
Tollen's or Fehling's reagent, nor does it decolorize bromine water or Baeyer's
reagent. On drastic oxidation with chromic acid, it gives a carboxylic acid (B)
having molecular formula 
.
Identify the compounds (A) and (5) and explain the reactions involved.
[3]
(b) Write chemical reactions to affect the following
transformations.
(i) Cyclohexene to adipic acid.
(ii) 3-bromonitrobenzene to 3-nitrobenzoic
acid. [2]
Or
(a) Write down the functional isomers of a carbonyl
compound with molecular formula 
. Which
isomer will react faster with HCN and why ? Explain the mechanism of the
reaction also. Will reaction lead to the completion with the conversion of
whole reactant into product at reaction conditions. If a strong acid is added
to the reaction mixture what will be the affect on concentration of the product
and why? [3]
(b) Arrange the following in decreasing order of their
acidic strength and give reason
for your answer.
Answer:
(a)
(i)
It gives orange ppt with 2,4-DNP reagent
Carbonyl group present, ketonic or aldehyde
(ii)
It neither reduces Tollen's reagent or Fehling's
solution
-CHO (aldehyde group absent)
(iii)
It forms yellow precipitate with
and
NaOH
group
present
(iv)
It does not decolourise
water
or Baeyer's reagent (alkaline 
)
or
in open
chain absent
(v)
Drastic oxidation gives a carboxylic acid (B)
B has ?COOH group
is 
[1]
Where R is 
Thus, A B is benzoic acid
[1]
Explanation
(b) (i) Cyclohexene to atopic acid
Ozonolysis by 
cleaves
(C = C) bond and ? COOH is formed.
(ii) 3 bromonitrobenzene to 3-nitrobenzoic acid
(a) Functional isomers (Carbonyl compounds) of the formula
are
(i)
propanone
(ii)
propanal
Both forms cyanohydrins with HCN.
Reaction with HCN is faster with propanal since steric
hindrance increases with (i)
Protonation increases electrophilic nature of carbonyl
compound.
In case of 
effect of
two methyl groups decrease positive charge on carbonyl carbon, hence its reactivity
for nucleophiric attack of CN- is decreased.
Hence, 
reacts
completely with HCN. [1]
Final products with HCN
Mechanism
Step I lonisation of weak acid in
presence of base 
Step II Nucleophilic addition of 
on
carbonyl compound
Step III 
(b)
No stabilization by resonance
is
stabilized by resonance
Thus, formation of 
is more
favoured than 
Thus, carboxylic acids are more acidic than alcohol lonisation
of 
is more
than 
since
electronegativity of 
F
shows more 
effect
than Cl. [1]
Thus,
Thus, decreasing acid strength is
[1]
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