COc1ccc(CNC(=O)c2c([S-])n(-c3ccc(C)cc3)c3cccc[n+]23)cc1
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?