Journal of the American Chemical Society, Vol.143, No.1, 41-45, 2021
Intramolecular London Dispersion Interactions Do Not Cancel in Solution
We present a comprehensive experimental study of a di-t-butyl-substituted cyclooctatetraene-based molecular balance to measure the effect of 16 different solvents on the equilibrium of folded versus unfolded isomers. In the folded 1,6-isomer, the two t-butyl groups are in close proximity (H center dot center dot center dot H distance approximate to 2.5 angstrom), but they are far apart in the unfolded 1,4-isomer (H center dot center dot center dot H distance 7 angstrom). We determined the relative strengths of these noncovalent intramolecular sigma-sigma interactions via temperature-dependent nuclear magnetic resonance measurements. The origins of the interactions were elucidated with energy decomposition analysis at the density functional and ab initio levels of theory, pinpointing the predominance of London dispersion interactions enthalpically favoring the folded state in any solvent measured.