O=C(Nc1nc2n(n1)C(c1ccccc1)C=C(c1ccccc1)N2)c1ccc(Cl)c([N+](=O)[O-])c1
The negative base-10 logarithmic of dissociation constant (pka) for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the pKa value is directly proportional to the standard Gibbs free energy change for the reaction. What is the pka value of this molecule?