J & K CET Medical J & K - CET Medical Solved Paper-2005

  • question_answer
    Bromination of alkanes involves:

    A)  carbanions        

    B)  carbocations

    C)  carbenes                           

    D)  free radicals

    Correct Answer: D

    Solution :

                    Bromination of alkanes in the presence of sunlight involves the formation of free radical. e.g.,       \[C{{H}_{4}}\xrightarrow[hv]{B{{r}_{2}}}C{{H}_{3}}Br\] Mechanism: Initiation:                 \[Br-Br\xrightarrow[{}]{hv}B{{r}^{\bullet }}+B{{r}^{\bullet }}\] Propagation:                 \[C{{H}_{4}}+B{{r}^{\bullet }}\xrightarrow{{}}CH_{3}^{\bullet }+HBr\]                 \[CH_{3}^{\bullet }+Br-Br\xrightarrow{{}}C{{H}_{3}}Br+B{{r}^{\bullet }}\] Termination:                 \[B{{r}^{\bullet }}+B{{r}^{\bullet }}\xrightarrow{{}}B{{r}_{2}}\]  


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