Charge transfer and electron localization as the origin of the anomeric effect in the O─C─O segment of dimethoxymethane and spiroketals

Charge transfer and electron localization as the origin of the anomeric effect in the O─C─O... Every day, more evidence accumulates, leading to the conclusion that the stereoelectronic model through the nO → σ*C─O interaction is of minor relevance or even inoperative to explain conformational preference in the specific O─C─O segment. In the present study, dimethoxymethane (DMM) and some model spiroketals were chosen to develop a reliable and easy to apply methodology that is simple to interpret by experimental chemists. The general conformation observed in these molecules, present in many biologically active natural products, is the gauche‐gauche (g,g) in DMM and bis‐diaxial in spiroketals. To study this conformational preference, this paper presents a new approach, where general trends for the atomic and molecular energetic components, as well as localization and delocalization indices, and their bonded (Δb) and nonbonded (Δnb) electronic contributions are analyzed. In addition, group contributions to the electron localization and polarization are also defined, agreeing with the conformational preference. It is clear that electronic localization/delocalization is capable of reproducing experimental observations, showing an adequate correlation of this property to the cos θ term in the context of Pople's analysis. It is proposed that electron delocalization between electronegative atoms or total delocalization between nonbonded atoms is not the major contributors to the axial conformational preference observed in spiroketals. Conformational preference shows defined trends in terms of group delocalization in DMM and ring localization and charge transfer between groups in spiroketals. This way, electronic delocalization can be used to evaluate the anomeric effect, using just a few parameters, which makes the method broadly functional. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Physical Organic Chemistry Wiley

Charge transfer and electron localization as the origin of the anomeric effect in the O─C─O segment of dimethoxymethane and spiroketals

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Publisher
Wiley Subscription Services, Inc., A Wiley Company
Copyright
Copyright © 2018 John Wiley & Sons, Ltd.
ISSN
0894-3230
eISSN
1099-1395
D.O.I.
10.1002/poc.3793
Publisher site
See Article on Publisher Site

Abstract

Every day, more evidence accumulates, leading to the conclusion that the stereoelectronic model through the nO → σ*C─O interaction is of minor relevance or even inoperative to explain conformational preference in the specific O─C─O segment. In the present study, dimethoxymethane (DMM) and some model spiroketals were chosen to develop a reliable and easy to apply methodology that is simple to interpret by experimental chemists. The general conformation observed in these molecules, present in many biologically active natural products, is the gauche‐gauche (g,g) in DMM and bis‐diaxial in spiroketals. To study this conformational preference, this paper presents a new approach, where general trends for the atomic and molecular energetic components, as well as localization and delocalization indices, and their bonded (Δb) and nonbonded (Δnb) electronic contributions are analyzed. In addition, group contributions to the electron localization and polarization are also defined, agreeing with the conformational preference. It is clear that electronic localization/delocalization is capable of reproducing experimental observations, showing an adequate correlation of this property to the cos θ term in the context of Pople's analysis. It is proposed that electron delocalization between electronegative atoms or total delocalization between nonbonded atoms is not the major contributors to the axial conformational preference observed in spiroketals. Conformational preference shows defined trends in terms of group delocalization in DMM and ring localization and charge transfer between groups in spiroketals. This way, electronic delocalization can be used to evaluate the anomeric effect, using just a few parameters, which makes the method broadly functional.

Journal

Journal of Physical Organic ChemistryWiley

Published: Jan 1, 2018

Keywords: ; ; ; ;

References

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