O=[N+]([O-])c1nn(-c2ccc(Cl)cc2)[n+]([O-])c1NCc1ccncc1
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?