CMC Medical CMC-Medical Ludhiana Solved Paper-2007

  • question_answer
    Acetic acid reacts separately with the following alcohols. The rate of esterification is highest for

    A)  \[C{{H}_{3}}OH\]                            

    B)  \[{{C}_{2}}{{H}_{5}}OH\]

    C)  \[{{(C{{H}_{3}})}_{2}}CHOH\]    

    D)  \[{{(C{{H}_{3}})}_{3}}COH\]

    Correct Answer: A

    Solution :

                    As the hydrocarbon part (R) of the alcohol increases, the tetrahedral intermediate (I) formed during esterification becomes more and more crowded and hence the rate of esterification decreases accordingly. Thus, the smallest alcohol, i.e.,\[C{{H}_{3}}OH\]reacts at the fastest rate \[C{{H}_{3}}-\overset{O}{\mathop{\overset{\mathbf{||}}{\mathop{C}}\,}}\,-OH\xrightarrow{{{H}^{+}}}C{{H}_{3}}-\overset{{}^{+}OH}{\mathop{\overset{\mathbf{||}}{\mathop{C}}\,}}\,-OH\xrightarrow{ROH}\]\[\underset{\text{tetrahedral}\,\text{intermediate}\,\text{(i)}}{\mathop{\left[ {{H}_{3}}C\,\,\,\underset{OR}{\overset{OH}{\mathop{\overset{\mathbf{|}}{\mathop{\overset{C}{\mathop{|}}\,}}\,}}}\,\,\,\,\,OH \right]}}\,\xrightarrow{-{{H}_{2}}O}\underset{\text{ester}}{\mathop{C{{H}_{3}}-\overset{O}{\mathop{\overset{\mathbf{||}}{\mathop{C}}\,}}\,-OR}}\,\]


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