ROTATIONAL SPECTRA OF METHYL ETHYL AND METHYL PROPYL NITROSAMINES - CONFORMATIONAL ASSIGNMENT, INTERNAL-ROTATION AND QUADRUPOLE COUPLING

A structural determination of two carcinogenic nitrosamines, methyl et hyl and methyl propyl nitrosamine, was performed. Microwave spectra we re gathered from both a Stark cell spectrometer and a pulsed jet Fabry -Perot Fourier transform microwave spectrometer. Each rotational trans ition is split into quadrupole hyperfine components by two nitrogen nu clei. This quadrupole pattern is doubled by a low barrier methyl rotor which produces resolvable A and E states. Relational spectra were ass igned for one conformer of methyl ethyl nitrosamine and two conformers of methyl propyl nitrosamine. The lowest energy conformers of each co mpound, according to empirical force field calculations, were assigned . The structure found for methyl ethyl nitrosamine has the nitrosyl ox ygen on the methyl side with the terminal methyl group of the ethyl ch ain in the gauche position (OMG). Both conformers of methyl propyl nit rosamine have the same skeletal structure as the methyl ethyl compound ; one conformer has the terminal methyl of the propyl group in the ant i position (OMGA) while the other conformer has this methyl in the gau che position (OMGG(-)). Rotational constants and quadrupole coupling c onstants are reported for each assigned species. A barrier to internal rotation of the N-methyl group in each compound is also reported.