CONFORMATIONAL STUDIES OF ALKYL NITRITES USING LOW-TEMPERATURE C-13, O-17, AND N-14 NMR-SPECTROSCOPY - O-17 NMR OF N-SUBSTITUTED FORMAMIDES

Low-temperature C-13, O-17, and N-14 NMR studies of alkyl nitrites, RONO, show that NMR spectra of these nuclei can be used in assigning conformations. Signals for the E and Z conformations are well-resolved for the O-17 spectra in both the N=O and N-O regions, with the E isomers absorbing at higher frequency than the Z isomers. Compounds which were studied included R = methyl (1), ethyl (2), propyl (3), butyl (4), isopropyl (5), sec-butyl (6), and tert-butyl (7). The chemical shifts are suggested to be related to the longer-wavelength absorption of the E conformations in the UV spectra. The signals for E and Z isomers can also be seen in the low-temperature N-14 spectra, although there is some overlap of peaks, except for methyl nitrite. The E isomers also absorb at higher frequency in the N-14 and C-13 spectra. N-substituted formamides were studied by O-17 NMR, and the Z conformations of N-tert-butyl formamide and formanilide were found to absorb at higher frequency for these compounds.