Conformational analysis of cis- and trans-isomers of 2,5-dimethyl-1,3-dioxane

Configurational and conformational properties of the complex of 2,5-dimethyl- 1,3,2-dioxaborinane with hydroxyl anion

“…The 2,5-T 1 and 2,5-T 2 conformers of the (Z)-isomer differ in the orientation of the hydroxyl group relative to the heterocyclic ring. The results obtained confirm the similarity of the associates studied with the closest non-boron analogs (the substituted 1,3-dioxanes [7]) and open up additional possibilities for a detailed study of the stereochemistry of cyclic boron esters with a tetrahedral boron atom.…”

Computer simulation of conformational transformations of 1,3-dioxanes and their 2-sila and 2-bora analogs

“…The transition states correspond to halfchair, sofa, and symmetrical boat conformers. The trans isomer of XVI is more stable than the cis isomer by 0.6 kcal/mol, and the ∆G° value for the interconversion of the former (determined according to [23][24][25][26]) is 1.4 kcal/mol in favor of the diequatorial conformer [46].…”

Conformational analysis of 1,3-oxathiane

“…Recently it was shown by computer simulation that for 1,3-oxathianes the unusual direct chair-chair inversion takes place avoiding the intermediate flexible forms [38,39]. Such direction of conformational isomerization is absent in the series of 1,3-dioxanes and 1,3-dithianes [24][25][26][27][28][29][30][31][32][33][34], but it is possible for 1,3-dioxa-2-sila- [40] and 2-germacyclohexanes [41]. In this study carried out by means of nonempiric HF/6-31G(d), MP2/6-31G(d)/HF/6-31G(d) approximations and density functional PBE/3z methods within the frame of HyperChem [42] and PRIRODA [43] complexes of programs all possible conforma-tional transformations of unsubstituted 1,3-oxathiane I were revealed.…”

“…The most labile of the conformers corresponding to minimum points on the potential energy surface within the frames of all the calculated approximations is the 1,4-T (1,4-T inv ) form. This peculiarity typical also for non-substituted [23,24], 2-, 5-, and 2,5-disubstituted 1,3-dioxanes [25][26][27][28][29], non-substituted 1,3-dithiane [33,34], 1,3,2-dioxathian-2,2-dioxide [45], complexes of 2-methyl-and 2,5-dimethyl-1,3,2-dioxaborinanes with hydroxyl anions [46,47] is probably the most general characteristic of the conformational properties of symmetrically substituted six-membered 1,3-and 1,3,2-heterocyclic compounds. Besides, all conformational chair-flexible form transformations are characterized by positive changes in entropy ΔS which is observed also for 1,3-dioxane [23] and 1,3-dithiane [33].…”

“…With the help of non-empiric quantum-chemical approximations the evaluation of stereoelectronic interactions was obtained and the presence of homoanomeric effects in the 1,3-oxathiane ring was established [20,21]. But unlike cyclohexane [22], 1,3-dioxanes [22][23][24][25][26][27][28][29][30][31][32], and 1,3-dithiane [33, 34], pathways of conformational isomerization of 1,3-oxathiane molecules were not considered. In the majority of cases "chair-chair" inversion was postulated [6,[9][10][11][12][13], and in some cases the participation of flexible forms was suggested [14][15][16]18].…”