A carbonyl compound (A) on reaction with Grignard reagent (B) followed by hydrolysis gives an alcohol. This alcohol on reaction with (i) \(PBr_3\) and (ii) \(Zn/dil.~H^+\) gives an alkane. Photochemical chlorination of the alkane gives only one monochloro derivative. A and B respectively are:
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Whenever a question states that an alkane gives only one monochloro derivative, immediately think of highly symmetrical alkanes such as methane, ethane or neopentane. Then work backwards through the reaction sequence to identify the required alcohol and Grignard reagent.
