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NEET AIPMT SOLVED PAPER SCREENING 2011

  • question_answer
    In the following reactions, (I) \[\text{C}{{\text{H}}_{\text{3}}}-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{3}} &  \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{CH}}}\,-\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{OH} \end{smallmatrix}}{\mathop{\text{CH}}}\,-\text{C}{{\text{H}}_{\text{3}}}\xrightarrow[{}]{{{\text{H}}^{\text{+}}}\text{/Heat}}\] \[{{\left( \overset{\text{A}}{\mathop{\begin{align}   & \text{major} \\  & \text{product} \\ \end{align}}}\, \right)}^{\text{+}}}\left( \overset{\text{B}}{\mathop{\begin{align}   & \text{major} \\  & \text{product} \\ \end{align}}}\, \right)\] (ii)\[\text{A}\xrightarrow[\text{in}\,\text{absence}\,\text{of}\,\text{peroxide}]{\text{HBr,dark}}\] \[{{\left( \overset{\text{C}}{\mathop{\begin{align}   & \text{major} \\  & \text{product} \\ \end{align}}}\, \right)}^{\text{+}}}\left( \overset{\text{D}}{\mathop{\begin{align}   & \text{major} \\  & \text{product} \\ \end{align}}}\, \right)\] the major products (A) and (C) are respectively

    A) \[\text{C}{{\text{H}}_{\text{3}}}-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}\,\text{=}\,\text{CH}-\text{C}{{\text{H}}_{\text{3}}}\] and \[\text{C}{{\text{H}}_{\text{3}}}-\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{Br} \end{smallmatrix}}{\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,-\text{CH}{{ }_{\text{2}}}-\text{C}{{\text{H}}_{\text{3}}}\]

    B) \[\text{C}{{\text{H}}_{\text{3}}}-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}\,\text{=}\,\text{CH}-\text{C}{{\text{H}}_{\text{3}}}\]and \[\text{C}{{\text{H}}_{\text{3}}}-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}\,-\underset{\begin{smallmatrix}  | \\  \text{Br} \end{smallmatrix}}{\mathop{\text{CH}}}\,-\text{C}{{\text{H}}_{\text{3}}}\]

    C) \[\text{C}{{\text{H}}_{2}}=\,\,\,\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}\,-\text{C}{{\text{H}}_{2}}-\text{C}{{\text{H}}_{\text{3}}}\]and \[\text{C}{{\text{H}}_{\text{3}}}-\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{Br} \end{smallmatrix}}{\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,-\text{C}{{\text{H}}_{\text{2}}}-\text{C}{{\text{H}}_{\text{3}}}\]

    D) \[\text{C}{{\text{H}}_{\text{2}}}\text{=}\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}\,-\text{C}{{\text{H}}_{\text{2}}}-\text{C}{{\text{H}}_{\text{3}}}\]and \[\underset{\begin{smallmatrix}  | \\  \text{Br} \end{smallmatrix}}{\mathop{\text{C}{{\text{H}}_{\text{2}}}}}\,-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\,\text{CH}\,}}\,-\text{C}{{\text{H}}_{\text{2}}}-\text{C}{{\text{H}}_{\text{3}}}\]

    Correct Answer: A

    Solution :

    (I)\[\text{C}{{\text{H}}_{\text{3}}}-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{CH}}}\,-\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{OH} \end{smallmatrix}}{\mathop{\text{CH}}}\,-\text{C}{{\text{H}}_{\text{3}}}\] \[\xrightarrow[{}]{{{\text{H}}^{\oplus }}\text{/}}\text{C}{{\text{H}}_{\text{3}}}\underset{{{\text{2}}^{\text{o}}}\,\text{carbocation}}{\mathop{-\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{CH}}}\,-\underset{\oplus }{\mathop{\text{CH}}}\,-\text{C}{{\text{H}}_{\text{3}}}}}\,\xrightarrow[\text{shift}]{\text{1,2-hydride}}\]\[\underset{\text{(more}\,\text{stable}\,{{\text{3}}^{\text{o}}}\text{carbonium}\,\text{ion)}}{\mathop{\text{C}{{\text{H}}_{\text{3}}}-\underset{\oplus }{\overset{\begin{smallmatrix}  \text{C}{{\text{H}}_{\text{3}}} \\  | \end{smallmatrix}}{\mathop{\text{C}}}}\,-\text{C}{{\text{H}}_{\text{2}}}-\text{C}{{\text{H}}_{\text{3}}}}}\,\] \[\xrightarrow[{}]{-{{H}^{\oplus }}}C{{H}_{3}}\underset{major\,(A)}{\mathop{-\overset{\begin{smallmatrix}  C{{H}_{3}} \\  | \end{smallmatrix}}{\mathop{C}}\,=CH}}\,-C{{H}_{3}}\] \[+C{{H}_{3}}\underset{mionr\,\,(B)}{\mathop{-\overset{\begin{smallmatrix}  C{{H}_{3}} \\  | \end{smallmatrix}}{\mathop{C}}\,=CH}}\,=C{{H}_{2}}\] \[C{{H}_{3}}\underset{Major\,\,(A)}{\mathop{-\overset{\begin{smallmatrix}  C{{H}_{3}} \\  | \end{smallmatrix}}{\mathop{C}}\,=CH}}\,-C{{H}_{3}}\] \[\xrightarrow[\begin{smallmatrix}  in\,absence \\  of\,peroxide \end{smallmatrix}]{HBr\,(dark)}C{{H}_{3}}-\underset{Major\,(C)}{\mathop{\underset{\begin{smallmatrix}  | \\  Br \end{smallmatrix}}{\overset{\begin{smallmatrix}  C{{H}_{3}} \\  | \end{smallmatrix}}{\mathop{C}}}\,-}}\,C{{H}_{2}}-C{{H}_{3}}\] \[+C{{H}_{3}}-\underset{Major\,(D)}{\mathop{\underset{\begin{smallmatrix}  | \\  Br \end{smallmatrix}}{\overset{\begin{smallmatrix}  C{{H}_{3}} \\  | \end{smallmatrix}}{\mathop{C}}}\,-}}\,\underset{\begin{smallmatrix}  | \\  Br \end{smallmatrix}}{\mathop{CH}}\,-C{{H}_{3}}\]


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