Pseudo-diequatorial conformation preference in 3-substituted thietane-1-oxide: A theoretical study

Citation
Jg. Contreras et St. Madariaga, Pseudo-diequatorial conformation preference in 3-substituted thietane-1-oxide: A theoretical study, BOL SOC CH, 45(3), 2000, pp. 469-478
Citations number
27
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
BOLETIN DE LA SOCIEDAD CHILENA DE QUIMICA
ISSN journal
0366-1644 → ACNP
Volume
45
Issue
3
Year of publication
2000
Pages
469 - 478
Database
ISI
SICI code
0366-1644(200009)45:3<469:PCPI3T>2.0.ZU;2-U
Abstract
The interconversion between the two isomeric forms (cis and trans) of a ser ies of 3-substituted thietane -1-oxide derivatives have been theoretically studied by means of ab initio molecular orbital theory. The optimized geome tries were obtained at the HF/6-31G** level, whereas energies were calculat ed using several basis sets all including electron correlation at the secon d order Moller Plesset theory. To derive the thermodynamics of the cis doub le left right arrow trans interconversion, the energies calculated at MP2/6 -311++G** were used. To determine the effect of the substitution on C3, the chloro, methyl, ethyl and t-buthyl derivatives have been studied. Ab initi o calculations show that in all cases the cis isomer is more stable than th e trans regardless the size of the substituent. The axial preference (trans ) of the oxygen atom of the S=O group, found in six-membered heterocycles i s not found in the four-membered thietane-1-oxide (TOX). The 1,3 repulsive interaction and the H beta - electron pair on sulfur repulsion are unimport ant in the determination of the preferred geometry of these species, The H beta - O9 non-bonded interaction does determine the cis geometry to be the most stable one. A small solvent effect on the cis double left right arrow trans interconver sion is predicted for the 3-chloro and 3-methyl TOX, regardless the polarit y of the medium. Temperature exerts an important role inthe 3-chloro-TOX sy stem but just a small effect on the 3-alkyl derivatives. The use of the IR spectra in the S=O stretching modes regions is proposed to distinguish betw een cis and trans isomeric forms in 3-substituted TOX.