pKa explanation through empirical formula?
Can we explain the above pka with (ONLY) the knowledge of the given
  numbers of atoms of C, H and O using the theory of Usanovich


No, nobody's theory (including Usanovich's) can explain $\ce{pK_{a}}$ differences based on molecular formula coefficients.  This is best illustrated by the observation that even compounds with the same coefficients (same values for "abcdef") can have different $\ce{pK_{a}}$ values.  For example, $\ce{C3H6O}$

\begin{aligned}
\ce{&amp;acetone &amp;&amp;pK_{a}=20}\\
\ce{&amp;allyl~ alcohol &amp;&amp;pK_{a}=$15.5$}\\
\end{aligned}