$\mathop C\limits_{\mathop |\limits_{COOH} } {H_2}\, - \,\,\mathop {\mathop C\limits^{\mathop |\limits^{OH} } }\limits_{\mathop |\limits_{COOH} } \,\, - \,\,C{H_2}\,\, - \,\,\mathop C\limits_{\mathop {||}\limits_O } \,\, - \,\,OH$
$\begin{array}{*{20}{c}}
{\,\,\,\,\,\,CHO} \\
{|\,\,\,} \\
{H - C - OH} \\
{|\,\,\,\,} \\
{\,\,\,\,\,\,\,\,\,C{H_2}OH}
\end{array}$