S=C(NCCCN(Cc1ccc(Cl)c(Cl)c1)c1ccc(Br)cn1)NCCc1c[nH]cn1
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?