question_answer

In the following sequence of reactions, which is incorrect \[C{{H}_{2}}=CH-CH=C{{H}_{2}}\xrightarrow[80{}^\circ C]{HBr}\text{ }A\xrightarrow{HBr}B\]                         \[\xrightarrow{Mg}C\]

A) A is \[C{{H}_{3}}-CH=CH-C{{H}_{2}}Br\]

B) B is \[C{{H}_{3}}CHBr-C{{H}_{2}}-C{{H}_{2}}-Br\]

C) C is cyclopropyi methane

D) B on \[{{S}_{N}}2\] with aqueous \[NaOH\] gives \[C{{H}_{3}}CHOH.C{{H}_{2}}C{{H}_{2}}Br\] and not \[C{{H}_{3}}CHBr.C{{H}_{2}}C{{H}_{2}}OH\]

Correct Answer: D

Solution :

[d] A is 1, 4-addition product due to conjugation B is obtained by further addition of HBr.\[(C{{H}_{3}}CHBr.C{{H}_{2}}.C{{H}_{2}}Br)\]. B gives C by cyclisation . If B reacts by \[{{S}_{N}}2\]mechanism, Br on \[1{}^\circ \]  carbon must be replaced by \[O{{H}^{-}}\] to give \[C{{H}_{3}}CHBr-C{{H}_{2}}-C{{H}_{2}}OH.\]