NEET Chemistry NEET PYQ-Haloalkanes and Haloarenes

  • question_answer
    Iodoform test is not given by:       [AIPMT 1998]

    A) 2-pentanone

    B) ethanol

    C) ethanol

    D) 3-pentanone

    Correct Answer: D

    Solution :

    [d] Iodoform test is given by compounds which have
                \[\begin{align}   & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,H \\  & C{{H}_{3}}-CO-group\,\,or\,C{{H}_{3}}-\overset{|}{\mathop{\underset{|}{\mathop{C}}\,}}\,-group. \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,OH \\ \end{align}\]
                Hence, 2-pentanone, \[{{C}_{2}}{{H}_{5}}CHO\] and \[{{C}_{2}}{{H}_{5}}OH\] give this test \[C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}COC{{H}_{3}}\]   
                2-pentanone and 3-pentanone \[C{{H}_{3}}C{{H}_{2}}COC{{H}_{2}}C{{H}_{3}}\] does not give idoform test.
                \[C{{H}_{3}}-COC{{H}_{2}}-C{{H}_{2}}-C{{H}_{3}}+3{{I}_{2}}+4NaOH\]\[\to \,\,\underset{\begin{smallmatrix}  Iodoform\, \\  (Yellow\,ppt.) \end{smallmatrix}}{\mathop{CH{{I}_{3}}}}\,\downarrow \,+\,C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}COONa\]\[+3NaI+3{{H}_{2}}O\]
                \[C{{H}_{3}}-CHO+3{{I}_{2}}+4NaOH\xrightarrow[{}]{{}}\]\[\underset{\begin{smallmatrix}  Iodoform\, \\  (yellow\,ppt) \end{smallmatrix}}{\mathop{CH{{I}_{3}}}}\,\downarrow \,\,+HCOONa\]\[+3NaI+3{{H}_{2}}O\]
                \[{{C}_{2}}{{H}_{5}}OH+4{{I}_{2}}+6NaOH\xrightarrow[{}]{{}}\underset{\begin{smallmatrix}  Iodoform \\  (yellow\,ppt). \end{smallmatrix}}{\mathop{CH{{I}_{3}}}}\,\,\,\downarrow \]     \[+HCOONa+5NaI+5{{H}_{2}}O\]
                In it following reaction is posses
                \[({{C}_{2}}{{H}_{5}}OH\xrightarrow[{}]{{{I}_{2}}}C{{H}_{3}}-CHO\xrightarrow[{}]{{{I}_{2}}+NaOH}CH{{I}_{3}})\]
                \[C{{H}_{3}}-C{{H}_{2}}-CO-C{{H}_{2}}-C{{H}_{3}}+{{I}_{2}}\]\[+NaOH\xrightarrow[{}]{{}}No\,reaction\]


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