O=C(NN1C(=O)/C(=C/c2nc3ccccc3[nH]2)SC1=S)c1ccccc1Cl
An acid's negative base-10 logarithmic dissociation constant (pka) follows directly from its underlying thermodynamics; pKa is directly proportional to its standard Gibbs free energy change. What is the pka value of this molecule?