Intermolecular Non-Covalent Carbon-Bonding Interactions with Methyl Groups: A CSD PDB and DFT Study

摘要

A systematic evaluation of the CSD and the PDB in conjunction with DFT calculations reveal that non-covalent Carbon-bonding interactions with X–CH3 can be weakly directional in the solid state (P ≤ 1.5) when X = N or O. This is comparable to very weak CH hydrogen bonding interactions and is in line with the weak interaction energies calculated (≤ –1.5 kcal·mol⁻¹) of typical charge neutral adducts such as [Me3N-CH3···OH2] (>2a). The interaction energy is enhanced to ≤–5 kcal·mol⁻¹ when X is more electron withdrawing such as in [O2N-CH3··O=C^dme] (>20b) and to ≤18 kcal·mol⁻¹ in cationic species like [Me3O⁺-CH3···OH2]⁺ (>8a).