anomeric effect

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If a pyranose ring has an electronegative substituent at the anomeric carbon then this substituent is more likely to take the axial configuration than the equatorial configuration. This is a consequence of a general effect (the generalized anomeric effect) that in a chain of atoms X-C-Y-C, in which Y and X are atoms with nonbonding electron pairs (e.g. F, O, N), the synclinal conformation is more likely. For example, in the compound CH3–O-CH2Cl, rotation can occur along the O-C bond. The conformation in which the chlorine atom is closer to the methyl group is preferred (the lone pairs on the oxygen atom act as groups in determining the conformation).

Subjects: Chemistry.

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