ISSN:
0192-8651
Keywords:
Computational Chemistry and Molecular Modeling
;
Biochemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Computer Science
Notes:
Optimized equilibrium geometries and rotational transition structures for CH3OCH XCH2 (X = H, F, CH3, NH2) and CH3OCF2CH2 radicals are obtained by using unrestructed Hartree-Fock (UHF) and second-order Møller-Plesset perturbation (UMP2) theory; a standard 6-31G* basis set is used for geometry optmizations; single-point energies for all stable rotamers are obtained at the UMP4/6-31 + G*//UMP2/6-31G* level. By analysis of rotamers, it is apparent that an anomeric effect exists for X = F and to a lesser extent for X = NH2. Several isodesmic reactions have been studied for the purpose of obtaining theoretical heats of formation and stabilization energies (SE) of these β substituted radicals and their α isomers; the examination of computed SE shows that in the case of CH3OCHFCH2 and CH3OCF2CH2 radicals, a significant extra stabilization induced by the anomeric effect occurs. The question of nO → σCX* negative hyperconjugation in β-substituted radicals was explored with the aid of natural bond orbital (NBO) energetic analysis; it appears that nO → σCF* delocalization plays a predominant role in the conformational preference and stabilization of β fluoro derivatives; on the other hand, the stabilization arising from the oxygen lone pair into the σCN(H2)* orbital does not appear to be the key factor in the conformational preference of the CH3OCHNH2CH2 radical. © 1994 by John Wiley & Sons, Inc.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcc.540151204
