Substituent effects in intermolecular C(sp3)-H ⋯ O(sp3) contacts: how strong can a C(sp3)-H ⋯ O(sp3) hydrogen bond be?

The dependence of the strength of the C(sp3)-H ⋯ interaction, with functional groups attached to the carbon atom, has been investigated for various families of R1R2R3CH ⋯ OH2 model complexes, totalling 14 model complexes, the simplest of which is CH4 ⋯ OH2. The study has ben carried out using the Hartree-Fock and second-order Møller-Plesset methods, and also with the Becke-Lee-Yang-Parr (B-LYP) functional. The substituent effect can be important. Thus, the C(sp3)-H ⋯ O(sp3) interaction becomes eight times stronger (−2.41 kcal/mol) when R1 = R2 = R3 = F than when R1 = R2 = R3 = H. The B-LYP functional reproduces the trends but the energies are always 0.7–1.2 kcal/mol weaker.