JEE Main & Advanced Chemistry Hydrocarbons Question Bank Alkane

  • question_answer What is the chief product obtained when n-butane is treated with bromine in the presence of light at \[{{130}^{o}}C\] [IIT-JEE 1995]

    A) \[\underset{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{3}}}{\mathop{\underset{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|}{\mathop{C{{H}_{3}}-C{{H}_{2}}-CH-Br}}\,}}\,\]

    B) \[\underset{C{{H}_{3}}\,\,\,\,\,\,\,\,}{\mathop{\underset{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{C{{H}_{3}}-CH-C{{H}_{2}}-Br}}\,}}\,\]

    C) \[\underset{\,\,\,\,\,\,\,\,\,C{{H}_{3}}}{\mathop{\underset{\,\,\,\,|}{\mathop{\overset{\,\,\,\,\,\,\,\,\,\,\,C{{H}_{3}}}{\mathop{\overset{\,\,\,\,\,\,|}{\mathop{C{{H}_{3}}-C-Br}}\,}}\,}}\,}}\,\]

    D) \[C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-Br\]

    Correct Answer: A

    Solution :

               \[C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{3}}+B{{r}_{2}}\underset{\,\,\,\,{{130}^{o}}C}{\mathop{\xrightarrow{\text{Light}}}}\,\]\[\underset{\begin{smallmatrix}  \text{2}-\text{Bromo}\,\text{butane}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{   } \\  \,\,\,\text{(Main}\,\text{product)} \end{smallmatrix}}{\mathop{C{{H}_{3}}-\underset{\underset{Br\,\,}{\mathop{|\,\,\,\,\,}}\,}{\mathop{CH}}\,-C{{H}_{2}}-C{{H}_{3}}}}\,+\underset{\begin{smallmatrix}  \text{1}-\text{Bromo}\,\text{butane} \\  \,\,\,\,\,\,\,\,\,\,\,\text{(Minor)} \end{smallmatrix}}{\mathop{C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-Br}}\,\] 2-Bromobutane is the main product because \[{{2}^{o}}\]carbonium ion is more stable than \[{{1}^{o}}\].


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