Methyl/Phenyl Attraction by CH/π Interaction in 1,2-Substitution Patterns

In 1,2-Me,Ph substitution patterns of organic compounds the methyl group attracts one of the phenyl sides to establish a CH/π bond with one of the <i>ortho</i> carbon atoms (the C_<i>o</i> side), leading to a characteristic tilting of the phenyl ring around its C_<i>i</i>–C_<i>p</i> axis. This phenyl rotation shortens the C_Me–C_<i>o</i> distances to bonding contacts between the methyl hydrogen atoms and the <i>ortho</i> carbon atom C_<i>o</i> well below the van der Waals distance of 3.70 Å. On the other hand, it elongates the C_Me–C_<i>o</i>′ distances outside of the reach of any CH/π interaction (>3.70 Å). Our study is based on a search in the Cambridge Structural Database for substructures Me–CC–Ph, Me–C–C–Ph, and Me–C–N–Ph with 1,2-Me,Ph substitution patterns. In the 1,2-Me,Ph substitution motif the torsion angle C_Me–C–C–C_<i>i</i> determines the length of the C_Me–C_<i>i</i> and C_Me–C_<i>o</i> distances. For aromatic compounds these torsion angles are close to 0°, but in five- and six-membered ring compounds and in open-chain compounds the torsion angles vary considerably. Universally, for torsion angles up to 80° CH/π bonds were found, whereas the long C_Me–C_<i>i</i> and C_Me–C_<i>o</i> distances for torsion angles >80° do not allow a CH/π interaction. The results of the present CSD analysis are supported by calculations