O=C(c1ccccc1)c1ccc2nc(Nc3ccccc3Cl)c3nncn3c2c1
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?