OLIGO(CYCLOHEXYLIDENE) OXIMES AND DERIVATIVES AS PROBE MOLECULES FOR LONG-RANGE SUBSTITUENT EFFECTS ON C-13 NMR CHEMICAL-SHIFTS

For a series of rodlike aliphatic oximes (1-4) the influence of the ox ime substituent on the C-13 NMR chemical shifts has been studied. Vari ous 2D NMR techniques were applied for the unequivocal assignment of t heir H-1 and C-13 resonances. For bicyclohexylidene oximes 1-2 long-ra nge substituent effects on the C-13 NMR chemical shifts of aliphatic c arbon atoms of the six-membered rings due to the presence of the oxime group are discernible up to positions six carbon-carbon bonds distant from the iminyl; carbon! The C-13 NMR data obtained for bicyclohexyl oximes 3-4 reveal that in this series the effect is limited to carbon atoms which are five bonds distant from the iminyl carbon. The observe d differences between the two series is attributed to the presence of an olefinic double bond in 1-2,: whch becomes polarized by the electri c field of the oxime substituent.