The proton magnetic resonance spectra of six-membered cyclic acetals. Part III. The vicinal coupling constants of alkyl-substituted 1,3-dioxans existing in non-chair conformations

Abstract

The 1H n.m.r. spectra of several 1,3-dioxans known to exist in non-chair conformation have been recorded in carbon tetrachloride, methylene chloride, benzene, or nitrobenzene solutions at 60 and 220 MHz. In all cases the values of the vicinal coupling constants are almost independent of temperature, and in several cases large (> 10 Hz) vicinal coupling constants, indicative of anancomeric twisted boat conformations are observed. The results lead to conclusions concerning the preferred boat conformations of the 1,3-dioxan ring, and the preferred orientations of substituents under this circumstance.