1 $\begin{array}{*{20}{c}}
{C{H_3} - C{H_2} - CH - COOH}\\
{\,\,\,\,|}\\
{\,\,\,\,\,\,\,OH}
\end{array}$
2 $\begin{array}{*{20}{c}}
{C{H_3} - CH - COOH}\\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\\
{\,\,\,\,\,\,\,\,\,C{H_2} - OH}
\end{array}$
3 $\begin{array}{*{20}{c}}
{C{H_3} - CH - COOH}\\
\,\,\,\,{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\\
\,\,\,\,{OH\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}$
4 $\begin{array}{*{20}{c}}
{C{H_3} - CH - C{H_2} - COOH}\\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\\
{OH\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}$