O=C(CCS(=O)(=O)c1cc2c(cc1Cl)NC(=O)CO2)NCc1ccc(Cl)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?