O=C1Nn2c(nc3c(c2=O)CCCC3)/C1=N/Nc1cccc(Cl)c1
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?