Uttarakhand PMT Uttarakhand PMT Solved Paper-2011

  • question_answer
    Identify Z in the following reaction sequence \[C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}OH\xrightarrow[160-180{}^\circ ]{conc.\,{{H}_{2}}S{{O}_{4}}}X\xrightarrow[{}]{B{{r}_{2}}}\]      \[Y\xrightarrow[(ii)\,NaN{{H}_{2}}]{(i)\,Alc.\,LOH}Z\]

    A)  \[C{{H}_{3}}CH(N{{H}_{2}})C{{H}_{2}}N{{H}_{2}}\]

    B)  \[C{{H}_{3}}CHOHC{{H}_{2}}OH\]

    C)  \[C{{H}_{3}}\underset{\begin{smallmatrix}  | \\  OH \end{smallmatrix}}{\mathop{C}}\,=C{{H}_{2}}\]

    D)  \[C{{H}_{3}}C=CH\]

    Correct Answer: D

    Solution :

     \[C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}OH\xrightarrow[160{}^\circ -180{}^\circ ]{{{H}_{2}}S{{O}_{4}}}\underset{(X)}{\mathop{C{{H}_{3}}CH=C{{H}_{2}}}}\,\xrightarrow[{}]{B{{r}_{2}}}\] \[\underset{(Y)}{\mathop{C{{H}_{3}}-\underset{\begin{smallmatrix}  | \\  Br \end{smallmatrix}}{\mathop{CH}}\,-\underset{\begin{smallmatrix}  | \\  Br \end{smallmatrix}}{\mathop{C{{H}_{2}}}}\,}}\,\xrightarrow[-HBr]{Alc.\,KOH}\underset{C{{H}_{3}}CH=CHBr}{\overset{C{{H}_{3}}CBr=C{{H}_{2}}}{\mathop{+}}}\,\] \[\xrightarrow[-HBr]{NaN{{H}_{2}}}\underset{(Z)}{\mathop{C{{H}_{3}}C\equiv CH}}\,\] \[NaN{{H}_{2}}\]being a stronger base than alcoholic KOH, readily brings about dehydrobromination of less reactive vinyl bromides to give propyne (Z).


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