O=C(CC(=O)Nc1ccccc1)N/N=C/c1cc(/N=N/c2ccc(Br)cc2)ccc1O
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?