A theoretical investigation of the effects of electronegative substitution on the strength of C-H⋯N hydrogen bonds

Abstract

The effects of electronegative substitution (as modeled using fluoro substituents) on the strength of C-H⋯N interactions, and how these effects change with hybridization or with acidity of the proton donor, are examined through the use of quantum chemistry. The binding energies (Do) in complexes between fluorinated derivatives of acetylene, ethylene, ethane and methane (the donors) and ammonia (the acceptor) are considered. We find that fluoro substitution leads to a strengthening of the C-H⋯N hydrogen bonds in all cases. The effect of replacing a beta hydrogen by fluorine increases as the hybridization of the proton donor goes from sp < sp2 < sp3. This trend is the opposite of the propensit..