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 CDCl(3) by the changes in the folded/unfolded ratios, as measured by (1)H 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.