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

Abstract

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.