S=C1NC2=C(COC/C2=C\c2ccccc2Cl)C(c2ccccc2Cl)N1
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?