O=C1CC2(CCC(O)(c3ccc(Cl)cc3)C(C(=O)c3ccc(Cl)cc3)C2)C(=O)c2ccccc2N1
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?