O=C(c1ccccc1)c1ccc2[nH]c(-c3c(Cl)c(Cl)c(Cl)c(Cl)c3C(=O)Nc3ccco3)nc2c1
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?