Publication Date:
2017-11-29
Description:
Every day, more evidence accumulates, leading to the conclusion that the stereoelectronic model through the n O 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 (Δ b ) and nonbonded (Δ nb ) 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. A new approach to study conformational preference with a reliable methodology that is simple to apply and interpret is presented. Trends for atomic and molecular energetic components, and localization and delocalization indices, and their electronic contributions are analyzed. Group contributions to electron localization and polarization agree with conformational preference. Electronic localization/delocalization reproduces experimental observations, showing adequate correlation to Pople's cos θ term. Electronic delocalization can be used to evaluate the anomeric effect, using few parameters, making the method broadly functional.
Print ISSN:
0894-3230
Electronic ISSN:
1099-1395
Topics:
Chemistry and Pharmacology
,
Physics
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