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

A systematic evaluation of the CSD and the PDB in conjunction with DFT calculations reveal that non-covalent Carbon-bonding interactions with X–CH(3) 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 [Me(3)N-CH(3)···OH(2)] (2a). The interaction energy is enhanced to ≤–5 kcal·mol(−1) when X is more electron withdrawing such as in [O(2)N-CH(3)··O=C(dme)] (20b) and to ≤18 kcal·mol(−1) in cationic species like [Me(3)O(+)-CH(3)···OH(2)](+) (8a).