CCOc1ccc(CCNC(=O)c2ccc(C[S+]([O-])Cc3ccc(Cl)cc3)o2)cc1OCC
An acid's negative base-10 logarithmic dissociation constant (pka) follows directly from its underlying thermodynamics; pKa is directly proportional to its standard Gibbs free energy change. What is the pka value of this molecule?