A Molecular Balance for Measuring Aliphatic CH−π Interactions

A series of conformationally flexible bicyclic N-arylimides were employed as molecular balances to study the weak aliphatic CH−π interaction between alkyl and arene groups. The formation of intramolecular CH−π interactions in the folded conformers was characterized by X-ray crystallography. The strengths of the interactions were characterized in CDCl3 by the changes in the folded/unfolded ratios, as measured by 1H NMR. The CH−π interaction between a methyl group and an aromatic surface was ∼1.0 kcal/mol and was easily disrupted or masked by conformational entropy and repulsive steric interactions.