Double proton transfers in complexes of formic acid with CH4, NH3, H2O, HF and H2

Abstract

Double proton migrations in complexes of formic acid with CH4, NH3, H2O, HF and H2 have been studied in the gas phase by ab initio (RHF/6–31G∗∗ and MP2/6–31G∗∗) calculations. The calculations show that the molecules HY, where H = CH3, NH2, OH, F and H, promote double proton migration in the complexes. The energy barriers calculated by the RHF/6–31G∗∗ (MP2/6–31G∗∗) method for these reactions are 74.0 (54.7), 19.9 (11.8), 26.4 (14.4), 20.2 (10.6) and 58.3 (46.0) kcal/mol, respectively. The height of the energy barrier of this reaction depends on the proximity of the two hydrogen bonds to the linear configuration and the bond configuration at Y to the corresponding ‘elemental’ SE2 transition state structure, as well as on the acidity (energy) of the Y-H bond and the basicity (proton affinity) of Y.