$1$ $\,.\,\,\,C{H_3}\, - \,\,\mathop C\limits_{\mathop {||}\limits_O } \,\, - \,\,H\,\,\,\,\,\,\,\,\,\,\,\,\,$
$2$ $\,.\,\,\,C{H_3}\, - \,\,\mathop C\limits_{\mathop {||}\limits_O } \,\, - \,\,C{H_3}\,\,\,\,\,\,\,\,\,$
$3$ $\,.\,\,C{H_3}\, - \,\,\mathop C\limits_{\mathop {||}\limits_O } \,\, - \,\,C{H_2}\, - \,\,\mathop C\limits_{\mathop {||}\limits_O } \,\, - \,\,H\,\,\,\,\,\,$
$4$ $\,.\,\,C{H_3}\, - \,\,\mathop C\limits_{\mathop {||}\limits_O } \, - \,\,C{H_2}\, - \,\mathop C\limits_{\mathop {||}\limits_O } \, - \,\,C{H_3}$
$\begin{array}{*{20}{c}}
{\,\,\,\,\,\,CHO} \\
{|\,\,\,} \\
{H - C - OH} \\
{|\,\,\,\,} \\
{\,\,\,\,\,\,\,\,\,C{H_2}OH}
\end{array}$