The Synergetic and Multifaceted Nature of Carbon-Carbon Rotation Reveals the Origin of Stability for Bulky Alkane Dimers

Designing compounds with as long carbon-carbon bond distances as possible to challenge conventional chemical wisdom is of current interest in the literature. These compounds with exceedingly long bond lengths are commonly believed to be stabilized by dispersion interactions. In this work, we build nine dimeric models with varying sizes of alkyl groups, let the carbon-carbon bond flexibly rotate, and then analyze rotation barriers with energy decomposition and information-theoretic approaches in density functional theory. Our results show that these rotations lead to extraordinarily elongated carbon-carbon bond distances and rotation barriers are synergetic and multifaceted in nature. The dominant factor contributing to the stability of the dimers with bulky alkane groups is not the dispersion force but the electrostatic interaction with steric and exchange-correlation effects playing minor yet indispensable roles.