An ab initio study of S(N)2 reactivity at C6 in hexopyranose derivatives. II. Role of populations, barriers, and reaction path curvature.
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.
Dawes
Richard
R
Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
Gough
Kathleen M
KM
Hultin
Philip G
PG
D002241:Carbohydrates / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D008958:Models, Molecular; D015394:Molecular Structure; D013816:Thermodynamics
D002241:Carbohydrates; D002244:Carbon