Proton Transfer in Ionic Hydrogen Bonds

Correlated electronic structure calculations, coupled with atoms in molecules analysis, have been employed in a study of proton transfer in ionic hydrogen bonds. The isoelectronic series FHF -, H 3 O 2 -, H 5 O 2 +, and N 2 H 7 + are used as models for such processes. Calculations at the MP2/6-311++G** level on the minimum energy structure and the transition state for proton transfer give an estimate of the barrier to proton transfer. Decomposition of the resulting charge distributions and energetics using Bader's techniques provides a deeper understanding of the electronic factors determining proton transfer barriers. It also indicates a fundamental difference between anionic and cationic hydrogen bonds.