Energy barriers to rotation in axially chiral analogues of 4-(dimethylamino)pyridine.
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.
Spivey, AC; Charbonneau, P; Fekner, T; Hochmuth, DH; Maddaford, A; Malardier-Jugroot, C; Redgrave, AJ; Whitehead, MA
Volume / Issue
Start / End Page
Electronic International Standard Serial Number (EISSN)
International Standard Serial Number (ISSN)
Digital Object Identifier (DOI)