O=C(CCC(=O)N1CCN(S(=O)(=O)c2ccc3ccccc3c2)CC1)Nc1cc(Cl)cc(Cl)c1
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?