JEE Main & Advanced Chemistry GOC Question Bank Structural and stereo isomerism

  • question_answer The number of possible enantiomeric pairs that can be produced during mono-chlorination of 2-methylbutane is [Pb. CET 2004]

    A) 3

    B) 4

    C) 1

    D) 2

    Correct Answer: D

    Solution :

    \[\overset{1}{\mathop{C}}\,{{H}_{3}}-\underset{C{{H}_{3}}\ }{\mathop{\underset{|}{\overset{2}{\mathop{C}}}\,H-}}\,\overset{3}{\mathop{C}}\,{{H}_{2}}-\overset{4}{\mathop{C}}\,{{H}_{3}}\] Its monochloro derivatives are as follows : (i) \[ClC{{H}_{2}}-\underset{C{{H}_{3}}\ \,}{\mathop{\underset{|}{\overset{\bullet }{\mathop{C}}}\,H-}}\,C{{H}_{2}}-C{{H}_{3}}\]  or \[C{{H}_{3}}-\underset{C{{H}_{2}}Cl\ \ \ \ \ \,}{\mathop{\underset{|}{\overset{\bullet }{\mathop{C}}}\,H-C{{H}_{2}}}}\,-C{{H}_{3}}\] It will exist as enantiomeric pair (d and l-forms) (ii) \[C{{H}_{3}}-\underset{C{{H}_{3}}\ \ \ \ \,}{\mathop{\overset{Cl\ }{\mathop{\underset{|}{\overset{|}{\mathop{C}}}\,-}}\,C{{H}_{2}}}}\,-C{{H}_{3}}\] no asymmetric C atom (iii) \[C{{H}_{3}}-\underset{C{{H}_{3}}\,}{\mathop{\underset{|}{\mathop{C}}\,H-}}\,\overset{Cl\ }{\mathop{\overset{|}{\mathop{C}}\,H}}\,-C{{H}_{3}}\] It will exist as enantiomeric pair (d- and l-forms) (iv) \[C{{H}_{3}}-\underset{C{{H}_{3}}\ }{\mathop{\underset{|}{\mathop{C}}\,H-}}\,C{{H}_{2}}-C{{H}_{2}}-Cl\] No asymmetric carbon atom Hence, only two enantiomeric pairs will be obtained by the monochlorination of 2-methylbutane.

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