Question

(A), (B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula C₄H₈O. Isomers (A) and (C) give positive Tollens' test whereas isomer (B) does not give Tollens' test but gives positive Iodoform test. Isomers (A) and (B) on reduction with Zn(Hg)/conc. HCl give the same product (D).

1) Write the structures of (A), (B), (C) and (D).

2) Out of (A), (B), and (C) isomers, which one is least reactive towards the addition of HCN?

Answer 1

Its given that A, B, C are non-cyclic functional isomers of a carbonyl compound and its M.F = C₄H₈O
So, A, B and C can be aldehyde or ketone

As A and C are giving positive Tollen's test ⇒ A and C are aldehydes

(A) CH₃CH₂CH₂CHO

(C) 

Its given that B doesn't give Tollen's test. ⇒ B is the ketone

As B gives positive Iodoform test

Hence, it is a methyl ketone i.e. –COCH₃ group is present

B = CH₃CH₂COCH₃

Hence

1) 

A = CH₃CH₂CH₂CHO

B = CH₃CH₂COCH₃

_{C =} 

D = CH₃CH₂CH₂CH₃

2) Isomer B i.e. butanone will be less reactive towards the addition of HCN because two bulky groups are present in the ketone. Moreover, electrophilicity of carbonyl carbon decreases due to the presence of electron releasing alkyl group.