O=C(N/C(=C/c1ccc(Cl)cc1)c1nc2ccccc2c(=O)n1Nc1ccc([N+](=O)[O-])cc1[N+](=O)[O-])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?