Source, of the anomeric effect

Results of molecular mechanics calculations were also used by us to explain the source of the anomeric effect in the Y—C—P=X (X, Y = O, S) system (79). As model compounds we chose 55,108, and 109 (Scheme 35). 

The dependence of the magnitude of the coupling constant Jc—p on the position of phosphorus in 2-P-substituted 1,3-diheteroanes was discussed in Section IV.B.3.b. While the argument supports ny-negative hyperconjugation as a source of the anomeric effect in 1,3-dioxane derivatives as well as in all phosphonium salts, the relationship between the Jc—p coupling constant through the axial and equatorial C(2)—P bonds in nonionic... 

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