$(1)\,\,{{(C{{H}_{3}})}_{3}}\bar{\ddot{C}}$
$(2)\,\,{{(C{{H}_{3}})}_{2}}\bar{\ddot{C}}$
$\,(3)\,\,C{{H}_{3}}\bar{\ddot{C}}{{H}_{2}}$
$(4)\,\,{{C}_{6}}{{H}_{5}}\bar{\ddot{C}}{{H}_{2}}$
$(I)$ $ CH_3 - NO_2$
$(II)$ $NO_2 - CH_2 - NO_2$
$(III)$ $ CH_3 - CH_2 - NO_2 $
$(IV)$ $\begin{array}{*{20}{c}}
{N{O_2} - CH - N{O_2}} \\
{|\,\,\,\,\,\,} \\
{\,N{O_2}}
\end{array}$
$(II)\,\,\,{{H}_{2}}C=CH-C{{H}_{2}}-\overset{+}{\mathop{C}}\,H-C{{H}_{3}}$
$(III)\,\,\,\begin{matrix}
\,\,\,\,\,C{{H}_{3}}\, \\
|\, \\
{{H}_{3}}C-C-\overset{+}{\mathop{C}}\,{{H}_{2}} \\
|\, \\
\,\,\,C{{H}_{3}} \\
\end{matrix}$