Conformational analysis of peracetylated hexononitriles

The conformations of six peracetylated hexononitriles in solution have been investigated by Fourier-transform, proton n.m.r. spectroscopy at 90 MHz, with iterative analysis and simulation of many of the spectra. The conformation of tetra-O-acetyl-L-arabinononitrile has been re-examined by the same methods. A shift reagent [Eu(fod)₃-d₃₀] and spectra at 220 MHz were used to improve spectral dispersion, where necessary. For practically all of the derivatives studied, the vicinal, proton-proton coupling-constants are consistent with a zigzag conformation in which the cyano group lies in the plane of the other carbon atoms of the chain, unless this conformation contains a parallel 1,3-interaction of substituents. Other conformers that are also consistent with the coupling constants observed are discussed, including rotamers about chain-terminal, carbon-carbon bonds.