Question

An alkyl halide by formation of its Grignard reagent and heating with water yields propane. What is the original alkyl halide ?

(a) Methyl iodide

(b) Ethyl iodide

(c) Ethyl bromide

(d) Propyl bromide

Answer 1

(d) Propyl bromide

Remember that in formation of an alkane from Grignard reagent, alkyl group always comes from Grignard reagent. Hence the number of carbon atoms in the Grignard reagent (and hence the corresponding alkyl halide from which this reagent is derived) and alkane formed from Grignard reagent will be identical.