Question

A carbonyl compound P (from i-iii), 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.

1.The structure of Q and R are respectively:

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Given: Carbonyl compound P gives iodoform test.
For a compound to give iodoform test, it should have a methyl ketone group ($C{H}_{3}CO$).
Among (i-iii). Only (ii) and (iii) have a methyl keto group hence, (ii) or (iii) can be the compound (P).
Further, we will proceed with possibilities of both (ii) and (iii).

'P' on reaction $C{H}_{3}MgBr$ gives a nucleophilic addition product.

Next step is dehydration with $H_{2}S{O}_4$ which is a E1 elimination reaction. From the option, we can say that dehydration occurs by a new ring formation.

Formed product 'Q' undergo ozonolysis to give dicarbonyl compound 'R'.

It is given that compound 'R' undergoes intramolecular aldol reaction. For a molecule to undergo aldol reaction, it should have an alpha hydrogen with respect to carbonyl group.

Compound 'R' from (iii) does not have an alpha hydrogen with respect to carbonyl group, hence, compound 'P' should be (ii).

Hence, the structure of 'Q' and 'R' is given in option (a).