Conformational analysis of 2-methyl-5-nitro-1,3,2-dioxaborinane

Quantum-chemical methods HF/6-31G(d), HF/6-31+G(d), MP2/6-31G(d)//HF/6-31G(d), and MP2/6-31+G(d)//HF/6-31+G(d) were used to investigate the conformational isomerization of 2-methyl-5-nitro-1,3,2-dioxaborinane. It has been shown that a potential energy surface of this compound includes two minima: an axial form of semi-chair and equatorial sofa together with a transition state belonging to the conformation of 2,5-twist-form. A comparison between experimental NMR ¹H and theoretical vicinal coupling constants was used to determine the quantitative conformational composition of cyclic boric acid ester and a value of ΔG ⁰ for nitro group at the ring carbon atom C⁵ in CCl₄ and C₆D₅NO₂ solutions.     

Molecular structure and conformational preference of 2-methyl-5-nitro-5-bromo-1,3,2-dioxaborinane and its complex with pyridine

The molecular structure of 2-methyl-5-nitro-5-bromo-1,3,2-dioxaborinane and its complex with pyridine is determined by single crystal X-ray diffraction. The structure of the synthesized compounds in the solution is also confirmed by the NMR spectroscopy data, and the conformational preference of their molecules is confirmed by the calculations using hybrid density functional theory.     

Conformational analysis of 2-isopropyl-5-methyl-5-methoxymethyl-1,3,2-dioxaborinane

Study of conformational transformations of 2-isopropyl-5-methyl-5-methoxymethyl-1,3,2-dioxaborinane using DFT approximation PBE/3ζ and the second order perturbation theory method RI-MP2/λ2 revealed beside the interconversion route sofa–sofa through a transition state corresponding to 2,5-twist form a number of local minima due to internal rotation of isopropyl and methoxymethyl substituents in sofa conformers. Over 88% of the molecules of the studied compound are present in a sofa form with the equatorially oriented CH₂OCH₃ group.     

Conformational analysis of 5-bromo-5-nitro-1,3-dioxane

Conformational analysis of 5-bromo-5-nitro-1,3-dioxane has been performed by computer simulation in terms of HF/pVDZ, hybrid DFT PBE/3ξ, and RI-MP2/λ2 quantum chemical methods. The global minimum on the potential energy surface corresponds to the chair conformer with axial nitro group, and the other two minima have been identified as chair conformer with equatorial nitro group and 2,5-twist. All transition states on the route of conformational transformations of the title molecule have been revealed.     

Conformational analysis of stereoisomers of 2,4-dimethyl-5-isopropyl-1,3,2-dioxaborinane

The investigation of conformation conversions of cis- and trans-isomers of 2,4-dimethyl-5-isopropyl-1,3,2-dioxaborinane using ab initio quantum-chemical approximation HF/6-31G(d) and the hybrid DFT-method PBE/3z showed that the routes of the transformations presuppose an equilibrium between sofa conformers with the different orientation of substituents at the atoms C⁴ and C⁵ of the ring that convert into each other through transition states corresponding to the equatorial and axial conformations of the 2,5-twist form. Based on experimental data of ¹H NMR spectra and calculated vicinal spin-spin coupling constants the quantitative conformational composition of cis- and trans-isomers was established and also the ΔG^o value of the conformation equilibrium was determined.     

Conformational composition of the 2,4,6-trimethyl-1,3,2-dioxaborinane stereoisomers

A study of conformational transformations of 2,4,6-trimethyl-1,3,2-dioxaborinane cis- and trans-isomers in non-empirical quantum-chemical HF/6-31G (d) and PBE/3z approximations showed that the transformation routes include the sofa conformers with different orientations of the substituents at the ring atoms C⁴ and C⁶ through the transition states corresponding to diequatorial, axial-equatorial, and dixial conformations of the 2,5-twist form. The calculation and ¹H NMR data show that the conformational equilibrium of cis-isomer is almost entirely shifted to diequatorial sofa, and the trans-form is characterized by the interconversion between the two axial-equatorial sofa conformers.     

Conformational analysis of 2,4,5-trimethyl-1,3,2-dioxaborinane individual stereoisomers

The study of the conformational isomerization of cis- and trans-isomers of 2,4,5-trimethyl-1,3-dioxaborinane I by means of RHF//STO-3G, 3-21G and 6-31G(d) quantumchemical methods led to the conclusion that its route includes equilibrium between sofa conformers with a different steric orientation of substituents at the C-4 and C-5 ring atoms. These conformers are interconverted through the maxima, the conformations of equatorial and axial 2,5-twist-forms. A comparison between experimental ¹H NMR and theoretical vicinal spin-spin coupling constants was used to determine the quantitative conformational composition of stereoisomers and a value of ΔG ⁰ for conformational equilibrium.     

Conformational analysis of the complex of 2-methyl-1,3,2-dioxaborinane with hydroxyl anion

Studies of the conformationsl transformations of the complex of 2-methyl-1,3,2-dioxaborinane with the hydroxyl anion performed by the quantum-chemical method HF/6-31+G(d) showed that they are more versatile than those in the initial boric ester, include the existence of six minima, five transition states, and are close to the conformational behavior of 1,3-dioxanes.     

Structure and conformational analysis of 2-hydroxy-5-isobutyl-1,3,2-dioxaborinane

The structure of 2-hydroxy-5-isobutyl-1,3,2-dioxaborinane, one of the major autooxidation products of 5-isobutyl-2-isopropyl-1,3,2-dioxaborinane, has been studied by ¹H, ¹³C, and ¹¹B NMR spectroscopy together with X-ray analysis. Molecules of the title compounds adopt a sofa conformation with equatorial isobutyl substituent. The ring interconversion path, free conformational energy, and optimal conformation of the isobutyl group (corresponding to the X-ray diffraction data) were determined by DFT quantum chemical calculations at the PBE/3ξ level of theory.     

Conformational analysis of 2-methyl-1,3,2-dioxaborinane in the presence of a water molecule

Russian Journal of Organic Chemistry - By means of nonempirical quantum-chemical approximations RHF//STO-3G, 3-21G, and 6-31G(d) conformational characteristics were studied of molecular associate...     

Conformational analysis of 2-methyl-1,3,2-dioxaborinane in the presence of an ammonia molecule

Nonempirical quantum chemical methods RHF//STO-3G, 3-21G and 6-31G(d) were used for the investigation of the conformational properties of molecular complexes of 2-methyl-1,3,2-dioxaborinane with ammonia (1:1). Two types of possible associates are revealed: with donor-acceptor N→B bond and with intermolecular NH···O hydrogen bond. Their calculated relative stability and conformational behavior are determined not only by the spatial orientation of the donor and the acceptor but also by the concepts of the used calculation approach.     

Reaction of 2-isobutyl-5-methyl-4-phenyl-1,3,2-dioxaborinane with acetonitrile

Reaction of 2-isobutyl-5-methyl-4-phenyl-1,3,2-dioxaborinane (a mixture ofcis- andtrans-isomers in a 81 : 19 ratio) with acetonitrile yielded 2,5-dimethyl-4-phenyl-5,6-dihydro1, 3-oxazine as a mixture ofcis- andtrans-forms in a 50 : 50 ratio. The possible mechanism of this transformation is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1297–1298, May, 1996.     

2-(5-Bromo-2-furyl)quinoxaline and 3-(5-bromo-2-furyl)-2-quinoxalone

2-(5-Bromo-2-furyl)quinoxaline and 3-(5-bromo-2-furyl)-2-quinoxalone were obtained by the action of bromine on the corresponding quinoxaline derivatives and also by condensation of o-phenylenediamine with, respectively, (5-bromo-2-furyl)glyoxal or (5-bromo-2-furyl)glyoxylic acid esters.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 404–406, March, 1973.