Charles A. Kingsbury

Conformations of cyclic and acyclic cyanides: 13C–H couplings

Natural abundance 13C n.m.r. spectra were determined for molecules such as methyl 1-cyano-4-oxo-2,6-diphenylcyclohexanecarboxylate and 4-oxo-1,2,6-triphenylcyclohexanecarbonitrile. The use of three-bond couplings between cyanide and hydrogen proved to be a useful tool in the assignment of configuration of cyclic molecules. In certain rigid molecules trans-13CN and H groups are characterized by a coupling of 9 Hz, whereas gauche-nuclei have a coupling of 2 Hz. In conformation ally mobile systems, the use of 1H vicinal couplings in conjunction with the 13C couplings provides strong evidence for preferred conformation. In certain highly substituted cyclohexanones, the importance of non-chair (probably twist-boat) conformers is evident.

Conformer preferences in aralkyl chloro-sulphides

Conformational preferences of the four isomers of 1-α-chlorobenzyl-2-phenylpropyl 2,4-dinitrophenyl sulphide are approximated from vicinal n.m.r. coupling constants. The ordering of groups at the carbons bearing chlorine and sulphur dominates the conformation of the entire molecule. The data are consistent with a possible attractive chlorine–hydrogen interaction when the bonds to carbon of these two groups are parallel. The reactivity of the four isomers is brimers is briefly discussed.