A) 2-chloro-3-methyl butane
B) 2, 2-dimethyl pentane
C) 2-chloro-2-methyl butane
D) None of the above
Correct Answer: C
Solution :
3-methyl-2-butanol on treatment with \[HCl\]gives 2-chloro-2-methyl butane. In this reaction a secondary carbocation is formed which changes to tertiary carbocation by rearrangement. Because tertiary carbocation is more stable than secondary carbocation. The mechanism of reaction is as \[C{{H}_{3}}-\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{C}}\,H-\underset{\begin{smallmatrix} | \\ OH \end{smallmatrix}}{\mathop{C}}\,H-C{{H}_{3}}+HCl\] \[\xrightarrow{{}}C{{H}_{3}}-\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{C}}\,H-\underset{\begin{smallmatrix} | \\ OH_{2}^{+} \end{smallmatrix}}{\mathop{C}}\,H-C{{H}_{3}}-C{{l}^{-}}\] \[C{{H}_{3}}-\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{C}}\,H-\underset{\begin{smallmatrix} | \\ OH_{2}^{+} \end{smallmatrix}}{\mathop{C}}\,H-C{{H}_{3}}\xrightarrow{-{{H}_{2}}O}\] \[\underset{secondary\text{ }carbocation}{\mathop{C{{H}_{3}}-\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{C}}\,H-\underset{+}{\mathop{C}}\,{{H}_{2}}C{{H}_{3}}}}\,\xrightarrow{\operatorname{Re}arrangement}\] \[\underset{\begin{smallmatrix} t-\text{ }carbocation \\ \left( more\text{ }stable \right) \end{smallmatrix}}{\mathop{C{{H}_{3}}-\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{\underset{+}{\mathop{C}}\,}}\,H-C{{H}_{2}}C{{H}_{3}}}}\,\xrightarrow{C{{l}^{-}}}\] \[\underset{2-chloro-2-methyl\text{ }butane}{\mathop{C{{H}_{3}}-CH-\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{\underset{\begin{smallmatrix} | \\ Cl \end{smallmatrix}}{\mathop{C}}\,}}\,{{H}_{2}}C{{H}_{3}}}}\,\]
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