An Orbital-Overlap Complement to Atomic Partial Charge

Angewandte Chemie - International Edition

5 years ago

An Orbital-Overlap Complement to Atomic Partial Charge

Arshad Mehmood, Benjamin G. Janesko

Atomic partial charges are widely used to predict reactivity. Partial charge alone is often insufficient: the carbons of benzene and cyclobutadiene, or those of diamond, graphene, and C60, possess nearly identical partial charges and very different reactivities. Our atomic overlap distance complements computed partial charges by measuring the size of orbital lobes that best overlap with the wavefunction around an atom. Compact, chemically stable atoms tend to have overlap distances smaller than chemically soft, unstable atoms. We show here how combining atomic charges and overlap distances captures trends in aromaticity, nucleophilicity, allotrope stability, and substituent effects. Applications to recent experiments in organic chemistry (counterintuitive Lewis base stabilization of alkenyl anions in anionic cyclization) and nanomaterials chemistry (facile doping of the central atom in Au7 hexagons) illustrate this combination's predictive power. The atomic overlap distance DA measures the characteristic size of the molecular orbital lobes around atom A. Unstable, weakly bound atoms often tend to have larger DA than stable, tightly bound atoms. The atomic overlap distance complements the atomic partial charge QC of carbon atoms in representative organic molecules, distinguishing anti-aromatic cyclobutadiene (top, larger DC) from aromatic molecules (bottom, smaller DC).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201702715