NEET Sample Paper NEET Sample Test Paper-14

  • question_answer 93) Decreasing order of reactivity in Williamson's ether synthesis of the following.
    (I)\[M{{e}_{3}}CC{{H}_{2}}Br\]
    (II)\[C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}Br\] 
    (III)\[C{{H}_{2}}=CHC{{H}_{2}}Cl\]
    (IV)\[C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}C{{H}_{2}}Cl\]

    A)  (I) > (II) > (IV) > (III)

    B)  (III) > (II) > (IV) > (I)

    C)  (I) > (III) > (II) > (IV)

    D)  (II) > (III) > (IV) > (I)

    Correct Answer: D

    Solution :

    The reactivity of alkyl halides is in the order, \[C{{H}_{3}}>{{1}^{o}}>{{2}^{o}}>{{3}^{o}}\]as tendency of alkyl halides to undergo elimination is\[{{3}^{o}}>{{2}^{o}}>{{1}^{o}}.\] C-Br bond length is longer than C-Cl bond. So, C-Br bond is easier to break than C-Cl bond. \[C{{H}_{2}}=CH\overset{\oplus }{\mathop{C}}\,{{H}_{2}}\] Carbocation is resonance stabilized. i.e., \[[C{{H}_{2}}=CH-\overset{\oplus }{\mathop{C}}\,{{H}_{2}}\leftrightarrow \overset{\oplus }{\mathop{C}}\,{{H}_{2}}-CH=C{{H}_{2}}]\]  So, it reacts faster than n-propyl choride.

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