A carbonyl compound P. which gives positive iodoform test, undergoes reaction with MeMgBr followed by dehydration to give an olefin Q. Ozonolysis of Q leads to a dicarbonyl compound R, which undergoes intramolecular aldol reaction to give predominantly S.
`Pundersetunderset("3. "H_(2)SO_(4),triangle)("2. "H^(+),H_(2)O)overset("1. "MeMgBr)toQunderset("2. "Zn,H_(2)O)overset("1. "O_(3))toRunderset("2. "triangle)overset("1. "OH^(-))toS`
The structure of the carbonyl compound P is

Options

A.
B.
C.
D.

Answer

B

Explanation

How to obtained the structures:
i. (P) gives Iodoform test, therefore, (P) must be a methyl ketone. From the structures given in (P) can be either (a) or (b).
ii. (a) and (b) in reaction with MeMgBr, followed by cyclisation would give products (Q) and (R ) respectively, products are either in (a) or in (b) in
iii. It is clear from the structure of (Q) and (R ), (S) can be either (b) or (c ) in
So proceed reverse from the (B) or (C ) from to check the products (R ) and (Q).
iv. Proceed reverse from product (b) of

v. Proceed reverse from the product (c ) in

vi. But the product (R )' is not given in any of the structures of . So the product (S) in is (b).
vii. Now proceed reverse form (R ) to get back the structure of (Q).

viii. From the structure of (Q), it is clear the compound (P) must be (b) in
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