Enantiomers computational studies

The side-arm alcohol plays a crucial role in controlling the reactivity and selectivity of the reaction. No reaction was observed if tetrahydrothiophene-derived sulfonium salts were used, or if the alcohol was protected as a methoxy group. The substrate is both activated and orientated by a hydrogen bond to its carbonyl group. No reaction intermediates were found in computational studies, so selectivity is determined in a single transition state. As before, controlling the ylide conformation and substrate approach determines the selectivity. The substrate approaches the ylide from the side bearing the alcohol in all cases, but 41a and 41b are predicted to present a different face of the ylide and so the opposite enantiomer is formed. 

Numerous theoretical treatments have been carried out to understand the mode of asymmetric induction of the Corey-Bakshi-Shibata (CBS) reduction, more thoroughly.12 Liotta et al. carried out computational studies to identify the transition states for CBS reductions of various ketones13 (Scheme 4.3k).In the asymmetric reduction of acetophenone with the catalyst (R)-28a, four transition states were found. Of the lowest energy is chairlike transition state A, which would lead to formation of the major enantiomer. In transition state A, the phenyl group of acetophenone occupies an equatorial position that is free from any steric interaction, as it is 5.5 A away from one of the two phenyl groups of the diphenylprolinol ring. On the other hand, transition state B, leading to the... 

An example of a QSERR study is by Carotti [39]. It involves the resolution of sulfoxides, 20, on a it-acid CSP containing (S,S)-N,N -(3,5-dinitrobenzoyl)-frans-1,2-diaminocyclohexane (DACH-DNB), 19a. After establishing capacity factors, k s and k R for the first and second eluted enantiomers, respectively, as well as determining the separation factors, a, the authors began their computational studies. They used a variety of electronic descriptors for the analytes including electrophilic superdelocalizabilities (S omo) and nucleophilic superdelocalizabilities of various key analyte atoms... 

A guanidine-catalysed enantiodivergent y-selective allylic amination of p,y-unsaturated thioesters has been developed.Both enantiomers can be obtained with excellent enantioselectivity (up to 93% ee) and high yield. Computational studies suggest that the reaction proceeds through a side-on mechanism with an s-trans dienolate. The study agrees well with experimental results and provides an intuitive explanation for the inversion of the absolute configuration. 

Fornarini, Matire, and co-workers110 have recently used Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry assaying the multiphoton dissociation behavior (IR-MPD) of the C3H7+ ion. This study has confirmed the conclusions of the computational results discussed above. The IR spectra recorded in solution and in a solid matrix display close resemblance to the spectral characteristics found by the IR-MPD study. Theoretical studies also indicated that the virtually free methyl rotation allows the interconversion of the two enantiomers of the isopropyl cation. 

In Section IV the computer simulation is extended to describe the effects of excitation in chiral molecules and racemic mixtures of enantiomers. The modification of the dynamical properties brought about by mixing two enantiomers in equimolar proportion may be explained in terms of rotation-translation coupling. The application of an external field in this context ai iplifies the difference between the field-on acf s and cross-correlation of enantiomer and racemic mixture and provides a method of studying experimentally the fundamental phenomenon of rotation-translation coupling in the molecular liquid state of matter. 

The accurate determination of the adsorption isotherm parameters of the two enantiomers on a CSP is of fundamental importance to do computer-assisted optimization to scale up the process. Such determinations are usually done with an analytical column and the most traditional method to determine the parameters and saturation capacity is by frontal analysis (see section 3.4.2). The aim of paper III was to investigate the adsorption behavior and the chiral capacity of the newly developed Kromasil CHI-TBB column using a typical model compound. Many of the previous studies from the group have been made on low-capacity protein columns which has revealed interesting information about the separation mechanism [103, 110, 111], For this reason a column really aimed for preparative chiral separations was chosen for investigation [134], As solute the enantiomers of 2-phenylbutyric acid was chosen. 

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