Conformational isomerization of polymethyl-substituted six-membered cyclic carbonates

Abstract

SHORT COMMUNICATIONSInterest in cyclic carbonates that are important products of chemical fixation of atmospheric carbon dioxide [1] is related to their specific conformational behavior [2-4] and possible applications for the synthesis of practically important copolymers [5,6] and in electrochemical processes [7,8]. In addition, these compounds can be used to synthesize chiral diols [9]. It was shown previously [10, 11] that, unlike classical 1,3-dioxanes, molecules of six-membered cyclic carbonates are characterized by lower number of stationary points on the potential energy surface (PES) and by a different character of energy minima (sofa instead of chair).The present communication reports on the results of quantum-chemical study on conformational isomerization of 4,4,6-trimethyl-and 4,4,6,6-tetramethyl-1,3-dioxan-2-ones I and II. The calculations were performed in terms of HF/6-31G(d), 6-31G(d,p), MP2/6-31G(d)// HF/6-31G(d), and MP2/6-31G(d,p)//HF/6-31G(d,p) approximations included into HyperChem software package [12].tions, the PES of cyclic carbonate II includes energydegenerate minima corresponding to unsymmetrical boat (UB) conformers which are interconverted through a transition state corresponding to sofa (S) conformer (Scheme 2, see table) .

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

“…The PES of 4,4,6-trimethyl-1,3-dioxan-2-one (XXIX) contains two minima (sofa and half-chair conformers) with similar energies, and the transition state has 2,5-T structure [75] (Scheme 16). The energy minima on the PES of 4,4,6,6-tetramethyl-1,3-dioxan-2-one (XXX) correspond to energy-degenerate unsymmetrical boat invertomers (UB) which are interconverted through the transition state having sofa (S) conformation [75].…”

“…The energy minima on the PES of 4,4,6,6-tetramethyl-1,3-dioxan-2-one (XXX) correspond to energy-degenerate unsymmetrical boat invertomers (UB) which are interconverted through the transition state having sofa (S) conformation [75].…”