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WB JEE Medical WB JEE Medical Solved Paper-2013

  • question_answer
    The order of stability of the following tatutomeric compound is \[\underset{I}{\mathop{C{{H}_{2}}=\,\overset{OH}{\mathop{\overset{|}{\mathop{C}}\,}}\,-C{{H}_{2}}-\overset{O}{\mathop{\overset{||}{\mathop{C}}\,}}\,-C{{H}_{3}}\rightleftharpoons }}\,\] \[\underset{II}{\mathop{C{{H}_{3}}-\,\overset{O}{\mathop{\overset{||\,\,\,}{\mathop{C}}\,}}\,-C{{H}_{2}}-\overset{O}{\mathop{\overset{||}{\mathop{C}}\,}}\,-C{{H}_{3}}\rightleftharpoons }}\,\] \[\underset{III}{\mathop{C{{H}_{3}}-\,\overset{O\,H}{\mathop{\overset{|}{\mathop{C}}\,}}\,=CH-\overset{O}{\mathop{\overset{||}{\mathop{C}}\,}}\,-C{{H}_{3}}\rightleftharpoons }}\,\]

    A)  I > II > III         

    B)  III > II > I

    C)  II>I> HI         

    D)  II > III > I

    Correct Answer: B

    Solution :

     The rolls of p-dicarbonyl compounds are more stable because of conjugation and intramolecular H-bonding. Thus, the order of stability is \[\underset{\text{III}}{\mathop{\underset{\begin{smallmatrix}  (Stabilised\,by\,conjugation \\  and\,H-bonding) \end{smallmatrix}}{\mathop{{{H}_{3}}C-\overset{OH}{\mathop{\overset{|}{\mathop{C}}\,}}\,=CH-\overset{O}{\mathop{\overset{|\,|}{\mathop{C}}\,}}\,-C{{H}_{3}}}}\,}}\,\]\[>C{{H}_{3}}-\overset{O}{\mathop{\overset{||}{\mathop{C}}\,}}\,-C{{H}_{2}}-\overset{O}{\mathop{\overset{|\,\,|}{\mathop{C}}\,}}\,-C{{H}_{3}}\]\[\underset{\begin{smallmatrix}  Less\,stable\,as(=)\,bond \\  is\,not\,conjugation\,with\,carbonyl\,group  \\  \text{I} \end{smallmatrix}}{\mathop{>C{{H}_{2}}=\overset{OH}{\mathop{\overset{|}{\mathop{C}}\,}}\,-C{{H}_{2}}-\overset{O}{\mathop{\overset{|\,|}{\mathop{C}}\,}}\,-C{{H}_{3}}}}\,\]


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