| Autor: |
Piscelli BA; University of Campinas, Chemistry Institute, Monteiro Lobato Street, Campinas, Sao Paulo 13083-862, Brazil. cormanich@unicamp.br., O'Hagan D, Cormanich RA |
| Jazyk: |
angličtina |
| Zdroj: |
Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2021 Mar 14; Vol. 23 (10), pp. 5845-5851. Date of Electronic Publication: 2021 Mar 10. |
| DOI: |
10.1039/d0cp06646j |
| Abstrakt: |
In this theory study we demonstrate the dominance of non-classical 1,3-diaxial CH ax OC hydrogen bonds (NCHBs) dictating a 'pseudo' anomeric effect in selectively fluorinated methoxycyclohexanes and also influencing the axial preference in the classical anomeric exhibitor 2-methoxytetrahydropyran, a phenomenon which is most often described as a consequence of hyperconjugation. Analogues of methoxycyclohexane where ring CH 2 's are replaced by CF 2 can switch to an axial preference and theory methods (NBO, QTAIM, NCI) indicate the dominance of 1,3-CH ax OMe interactions over hyperconjugation. For 2-methoxytetrahydropyran, it is revealed that the global contribution to the anomeric effect is from electrostatic interactions including NCHBs, not hyperconjugation, although hyperconjugation (n O →σ* CO or n O →σ* CC ) remains the main contributor to the exo-anomeric phenomenon. When two and three ether oxygens are introduced into the ring, then both the NCHB interactions and hyperconjugative contributions become weaker, not stronger as might have been anticipated, and the equatorial anomers progressively dominate. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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