O=C(NCCNC(=O)c1ccc(-c2ccc(Cl)c(Cl)c2)o1)c1cnccn1
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?