Nuclear magnetic resonance spectra of 2,7-dioxabicyclo[2,2,1]heptanes

Abstract

The n.m.r. spectra of nine substituted 2,7-dioxabicyclo[2,2,1]heptanes are discussed in terms of chemical shifts and coupling constants. The relative chemical shifts of endo- and exo-protons are the reverse of those in the analogous carbocyclic systems. The spectra are also characterised by a relatively large ⁴J(exo,exo)(3·0 c./sec.). There is strong diamagnetic shielding by a methyl group of an eclipsed vicinal proton. A clear-cut case of virtual coupling is presented for methyl 1,3,3-trimethyl-2,7-dioxabicyclo[2,2,1]heptane-6-endo-carboxylate.