title: An ab initio study of S(N)2 reactivity at C6 in hexopyranose derivatives. II. Role of populations, barriers, and reaction path curvature.
abstract: This paper continues our investigation into a simple dipole-dipole interaction model proposed to explain the dramatically reduced S(N)2 reactivity at the primary C6 position of galacto-configured pyranose systems relative to their gluco isomers. We present ab initio calculations (B3LYP/6-31+G(d,p)) on six model structures that show that this effect is not a major influence. Reactant rotameric equilibria as well as free-energy reaction barriers and reaction path curvature were evaluated. Results point to a number of other factors that could account for the observed reactivity differences. Our results cast doubt on the general relevance of transition structure dipole-dipole repulsions to S(N)2 reactivity.
authors.affiliation: Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Dawes
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Gough
authors.forename: Philip G
authors.initials: PG
authors.lastname: Hultin
mesh_terms: D002241:Carbohydrates / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D008958:Models, Molecular; D015394:Molecular Structure; D013816:Thermodynamics
chemical_list: D002241:Carbohydrates; D002244:Carbon