Conformation of 2,6- and 3,5-dichloroanisole from 1H and 2H nuclear magnetic resonance studies on liquid crystalline solutions

Abstract

The ¹H n.m.r. spectra of liquid crystalline solutions of the two dichloroanisoles labelled with ¹³C in the methyl groups have been analysed to yield sets of dipolar coupling constants, D_ij. It is shown that the D_ij values involving ¹³C and ring protons can be used to determine the minimum energy positions for reorientation about the ring–oxygen bonds independently of the nature of reorientation of the methyl protons about the oxygen–methyl bond. It is found that the minimum energy positions for the 3,5-dichloroanisole have all C and O atoms coplanar, whilst for the 2,6-dichloroanisole the COC and phenyl planes are orthogonal. The D_CH and D_HH values within the methyl groups are used to derive the HCH angles of 109.5 and 110.0 respectively, whilst using all the D_ij values fixes r_CH as 1.11 ± 0.03 and 1.14 ± 0.04 Å respectively. The ²H and ¹H n.m.r. spectra of compounds labelled with OCD₃ groups yield values for the quadrupole coupling constants of the C–D bonds of 132 ± 10 for 3,5- and 144 ± 24 kHz for 2,6-dichloroanisole.