Nc1ncnc2c1nc(Br)n2[C@H]1O[C@H]2COP(=O)(O)O[C@H]2[C@@H]1O
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?