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-pi Interaction between alkyl and arene groups. The formation of intramolecular CH-pi 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-pi interaction between a methyl group and an aromatic surface was similar to 1.0 kcal/mol and was easily disrupted or masked by conformational entropy and repulsive steric Interactions.