C[N+](C)(C)CC(=O)N/N=C(\C(=O)Nc1ccc(Cl)cc1)C1C(=O)N(c2ccccc2)N=C1N.[Cl-]
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?