(A), (B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula `C_4H_(8)O`. 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).
(a) Write the structures of (A), (B), (C) and (D).
(b) Out of (A), (B) and (C) isomers, which one is least reactive towards addition of HCN ?

Explanation

(a) Structures of A, B, C and D are given below :
`underset("Butanal-1")(A=CH_(3)CH_(2)CH_(2)CHO)`
`underset("Butan-2-one")(B=CH_(3)COCH_(2)CH_(3))`
`underset("2-Methylpropanal")(C=CH_(3)-underset(CH_(3))underset(|)(CH)-CHO)`
`underset("Butane")(D=CH_(3)CH_(2)CH_(2)CH_(3))`
(b) B i.e., `CH_3COCH_2CH_3` is the least reactive towards addition of HCN.