Experimental study of the cooperativity of CH-π interactions.

A series of new torsional molecular balances was designed to study the cooperativity of CH-π interaction in the solid state and in solution. The measured interaction energies correlated better to the number of participating alkyl carbons than to the number of CH-π contacts. The methyl and ethyl groups displayed additive interaction energies. However, the branched isopropyl group displayed strong positive cooperativity with higher than predicted interaction energies.