The carbon-13 nuclear magnetic resonance spectra of some 1,3-dioxans. Part II. A demonstration of non-chair conformations

Abstract

The ¹³C n.m.r. spectra of 36 1,3-dioxans are reported. Substituent effects on the chemical shifts of the ring carbon atoms are derived for a set of compounds known to exist in chair conformations. Using these effects to predict the chemical shifts in compounds that would have 4,6- or 2,4-syn-diaxial interactions in chair conformations results in large discrepancies between observation and prediction. It is concluded that such compounds exist to some extent in non-chair conformations.