The synthesis of specifically and selectively deuteriated 4,4′-bisalkoxyazoxybenzene derivatives

In connection with deuterium n.m.r. studies of molecular motion in liquid crystals we have developed a number of methods for the synthesis of selectively deuteriated 4,4′-bisalkoxyazoxybenzenes. This paper is concerned with (i) the labelling of specific methylene segments of the alkoxy-chains, (ii) the labelling of the aromatic nucleus, and (iii) the selective enrichment of the deuterium content of one alkoxy-chain relative to the other. Our studies of the n.m.r. spectra of these liquid crystals have shown that there is not (as has sometimes been supposed 1) a monotonic decrease in C–D quadrupole splitting in passing from the oxygen to the CD3 end of the alkoxy-chain. In [2H6]-PAA (p-azoxyanisole) we have also shown that the smaller splitting is associated with the CD3O group nearest to the NO end of the azoxy-group. Whereas the photorearrangement of azoxy-compounds is normally regiospecific, the photorearrangement of PAA selectively deuteriated in one methoxy-group is unusual in that it leads to isotopically scrambled products.