O=C(Cc1ccccc1)NN1C(=O)/C(=C\c2cccc([N+](=O)[O-])c2)S/C1=N\c1ccccc1
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?