$\begin{array}{*{20}{c}}
  {CHO} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {HOCH} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {C{H_2}OH} \\ 
  I 
\end{array}\,\,\,\,\,\,\,\,\,\,\,\,\,\,$$\begin{array}{*{20}{c}}
  {CHO} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {HOCH} \\ 
  | \\ 
  {C{H_2}OH} \\ 
  {II} 
\end{array}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,$$\begin{array}{*{20}{c}}
  {CHO} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {HCOH} \\ 
  | \\ 
  {C{H_2}OH} \\ 
  {III} 
\end{array}$

$\begin{align}
  & \begin{matrix}
   O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,  \\
   ||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,  \\
   H-O-C-C{{H}_{2}}-C{{H}_{2}}-CH-C{{O}_{2}}H  \\
   \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|  \\
   \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\underset{\oplus }{\mathop{N}}\,{{H}_{3}}  \\
\end{matrix}\,\,\,\,\,(p{{K}_{a}}=2) \\ 
 & (p{{K}_{a}}=4)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(p{{K}_{a}}=9) \\ 
\end{align}$