O=C(c1ccc2c(=O)n(Cc3ccccc3Cl)c(=S)[nH]c2c1)N1CCCC1
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?