O.R.D. characteristics of azido derivatives of pentoses

Abstract

O.r.d. curves of some methyl 4-azido-4-deoxypentopyranosides have been measured. Although it is not possible to predict, on the basis of analysis by an azide octant rule, the sign of the Cotton effect exhibited by these derivatives, several empirical observations are noteworthy. Those derivatives in the C1 ( d) conformation and having an axial azide substituent exhibit positive Cotton effects, whereas those having an equatorial azide substituent show negative Cotton effects. Azide derivatives in the 1C ( d) conformation and having an equatorial azide group exhibit a negative Cotton effect, whereas those having an axial azide substituent show a positive Cotton effect. There is a marked dependence of the magnitude of the background rotation on the configuration of the substituent at C-1; an axial, glycosidic, methoxyl group causes a much higher background rotation than does an equatorial substituent.