title: Distance-Dependent Attractive and Repulsive Interactions of Bulky Alkyl Groups.
abstract: The stabilizing and destabilizing effects of alkyl groups on an aromatic stacking interaction were experimentally measured in solution. The size (Me, Et, iPr, and tBu) and position (meta and para) of the alkyl groups were varied in a molecular balance model system designed to measure the strength of an intramolecular aromatic interaction. Opposite stability trends were observed for alkyl substituents at different positions on the aromatic rings. At the closer meta-position, smaller groups were stabilizing and larger groups were destabilizing. Conversely, at the farther para-position, the larger alkyl groups were systematically more stabilizing with the bulky tBu group forming the strongest stabilizing interaction. X-ray crystal structures showed that the stabilizing interactions of the small meta-alkyl and large para-alkyl groups were due to their similar distances and van der Waals contact areas with the edge of opposing aromatic ring.
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, 29208, USA.
authors.forename: Jungwun
authors.initials: J
authors.lastname: Hwang
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, 29208, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, 29208, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Smith
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, 29208, USA. shimizu@mail.chem.sc.edu.
authors.forename: Ken D
authors.identifier: 0000-0002-0229-6541
authors.initials: KD
authors.lastname: Shimizu
keywords: noncovalent interactions; stacking interactions; steric hindrance; substituent effects; supramolecular chemistry