Proton and carbon-13 NMR study of partially oriented 1,4-dioxane Determination of the r_α structure and of bond contributions to the orientation

Abstract

The proton and carbon-13 NMR spectra of 1,4-dioxane partially oriented in a nematic solvent were analysed, and the measured dipolar coupling constants, corrected for harmonic vibrations and for correlated deformation, were used to obtain information about the r _α structure of the molecule. It is concluded that the 1,4-dioxane molecule oscillates between two equivalent chair conformers, which can be described by a puckering amplitude of 0·55 Å. This study also indicates that each methylene group is bent away from the bisector of the ring angle towards the heteroatom. Finally, the molecular orientation of this molecule in N-(p-ethoxybenzylidene)-p′-n-butylaniline can be described by three bond interaction parameters: X_cc , X _v, X _CH (or X _CO), corresponding to the CC bonds, the virtual C₂C₆ and C₃C₅ bonds and the CH (or CO) bonds.