Aldehydes and Ketones - Result Question 42
####43. Base catalysed aldol condensation occurs with
$(1984,1 M)$
(a) propionaldehyde
(b) benzaldehyde
(c) 2-methyl propionaldehyde
(d) 2, 2-dimethyl propionaldehyde
Passage Based Questions
Passage 1
Two aliphatic aldehydes $P$ and $Q$ react in the presence of aqueous $K _2 CO _3$ to give compound $R$, which upon treatment with $HCN$ provides compound $S$. On acidification and heating, $S$ gives the product shown below :
(2010)
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Answer:
Correct Answer: 43. (c)
Solution:
- For base catalysed aldol condensation, there must be at least one $\alpha-H$ to carbonyl group.
$$ CH _3-CH _2-CHO \text {, } $$
$$ \begin{gathered} \text { Propionaldehyde } \ (2 \alpha-H) \end{gathered} $$
2, 2-dimethyl propionaldehyde (no $\alpha-H)$
Passage 1 (For Q. Nos. 44-46)
The given product is an ester, obtained by condensation of a hydroxy acid obtained through hydrolysis of a cyanohydrin :
Acid above is obtained by acid hydrolysis of cyanohydrin $S$ as
$S$ is obtained by nucleophile addition of HCN on $R$, hence $R$ is
$R$ is obtained by treatment of $P$ and $Q$ with aqueous $K _2 CO _3$ through aldol condensation reaction as
Passage 2 (For Q. Nos. 47-49)
(gives positive iodoform test)
R
$S$
Passage 3 (For Q. Nos. 50-52)
