$(I)$         $C{H_2} = CH\mathop C\limits^ +  HC{H_3}$

$\begin{array}{*{20}{c}}
  {{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,} \\ 
  {(II)\,\,\,\,\,\,\,\,\,\,C{H_2} = C - \mathop {{\text{ }}C}\limits^ +  {H_2}} 
\end{array}$    

$(III)$      $C{H_3}CH = CH\mathop C\limits^ +  {H_2}$