Theoretical studies for strong hydrogen bonds in trimethyl phosphate-(HNO3)n complexes, n = 1-3

Abstract

We have calculated energies and structures for the hydrogen bonded clusters between trimethyl phosphate and nitric acids. The hydrogen bond lengths between phosphoryl oxygen and the proton of nitric acid are short compared to normal hydrogen bonds, and the H-bond strengths are fairly strong. The hydrogen bond length becomes longer, and the strength becomes weaker, as more nitric acids are bound to the TMP. The average H-bond strengths for the TMP-(HNO3)n, complexes with n = 1, 2, and 3, are 9.6, 7.9 and 6.4 kcal/mol at 300 K, respectively. Weak hydrogen bonds between nitrate oxygen and methyl proton might contribute to the stability of the clusters. Not only the BSSE but also the fragment relaxation energies should be considered to calculate hydrogen bond strengths for the complexes accurately.