O=C(NCc1ccco1)c1ccc2c(c1)N(Cc1cccc(Cl)c1)C(=O)c1ccccc1[S+]2[O-]
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?