O=C1Nc2ccccc2/C1=C1/SC(=S)N(NC(=O)c2cccc(O)c2)C1=O
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?