Question

Predict the product C obtained in the following reaction of butyne-1.

\[\ce{CH3CH2 - C ≡ CH + HCl -> B ->[HI] C}\]

Options

• \[\begin{array}{cc}
  \phantom{.................}\ce{I}\\
  \phantom{.................}|\\
  \ce{CH3 - CH2 - CH2 - C - H}
  \\
  \phantom{.................}|\\
  \phantom{.................}\ce{Cl}
  \end{array}\]

• \[\begin{array}{cc}
  \phantom{...}\ce{I}\\
  \phantom{...}|\\
  \ce{CH3 - CH2 - CH - CH2Cl}
  \end{array}\]

• \[\begin{array}{cc}
  \phantom{.....}\ce{I}\\
  \phantom{.....}|\\
  \ce{CH3CH2 - C - CH3}\\
  \phantom{.....}|\\
  \phantom{.....}\ce{Cl}
  \end{array}\]

• \[\begin{array}{cc}
  \ce{CH3 - CH - CH2CH2I}\\
  |\phantom{.......}\\
  \ce{Cl}\phantom{.......}
  \end{array}\]

Answer 1

\[\begin{array}{cc}
\phantom{.....}\ce{I}\\
\phantom{.....}|\\
\ce{CH3CH2 - C - CH3}\\
\phantom{.....}|\\
\phantom{.....}\ce{Cl}
\end{array}\]

Explanation:

According to Markownikoff's rule, when an unsymmetrical alkene undergoes hydrohalogenation, the negative part goes to the C-atom with the least number of H-atoms.

\[\begin{array}{cc}
\phantom{...................................................................}\ce{I}\\
\phantom{...................................................................}|\\
\ce{CH3 - CH2 - C ≡ CH + HCl -> CH3 - CH2 - C = CH2 ->[HI] CH3 - CH2 - C - CH3}\\
\phantom{........................................}|\phantom{...........................}|\phantom{}\\
\phantom{.........................................}\ce{Cl}\phantom{.........................}\ce{Cl}\phantom{}
\end{array}\]