a
Alkyl halide on heating with alcoholic \(K O H\) undergoes dehydrohalogenation to yield alkene. If in reaction, more than one alkene is formed, then according to Saytzeff rule, the most highly substituted alkene formed is the major product,

\(\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,\,H} \\ 
  {\,\,\,\,\,\,\,\,\,|} \\ 
  {C{H_3} - CH - CH - C{H_3}} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {\,\,Br\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} 
\end{array}\xrightarrow[{Alc.KOH}]{{ - {H_2}O}}\) \(\left[ {\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,H - OH} \\ 
  {\,\,\,\,|} \\ 
  {C{H_3}CH = CH - C{H_3}} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {Br\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} 
\end{array}} \right] \to \mathop {C{H_3} - CH = CH - C{H_3}}\limits_{(Major\,product)}  + B{r^ - }\)