title: Energy barriers to rotation in axially chiral analogues of 4-(dimethylamino)pyridine.
abstract: The barriers to enantiomerization of a series of axially chiral biaryl analogues of 4-(dimethylamino)pyridine (DMAP) 1-10 were determined experimentally by means of dynamic HPLC measurements and racemization studies. The barriers to rotation in derivatives 1-6 (based on the bicyclic 5-azaindoline core) were lower than those in the corresponding derivatives 7-10 (based on the monocyclic DMAP core). Semiempirical (PM3), ab initio Hartree-Fock (HF/STO-3G), and density functional theory (DFT/B3LYP/6-31G*) calculations reveal that these differences in barriers to rotation are the result of differing degrees of hybridization of the non-pyridyl nitrogen in the enantiomerization transition states (TSs). The importance of heteroatom hybridization as a factor in determining nonsteric contributions to barriers to rotation in azabiaryls of this type is discussed.
authors.affiliation: Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK. a.c.spivey@sheffield.ac.uk
authors.forename: A C
authors.initials: AC
authors.lastname: Spivey
authors.forename: P
authors.initials: P
authors.lastname: Charbonneau
authors.forename: T
authors.initials: T
authors.lastname: Fekner
authors.forename: D H
authors.initials: DH
authors.lastname: Hochmuth
authors.forename: A
authors.initials: A
authors.lastname: Maddaford
authors.forename: C
authors.initials: C
authors.lastname: Malardier-Jugroot
authors.forename: A J
authors.initials: AJ
authors.lastname: Redgrave
authors.forename: M A
authors.initials: MA
authors.lastname: Whitehead