MICROWAVE-SPECTRA AND STRUCTURES OF CIS-METHYL NITRITE AND TRANS-METHYL NITRITE - METHYL BARRIER IN TRANS-METHYL NITRITE

Accurate structures for both cis- and trans-methyl nitrite have been derived from isotopic measurements for each atomic position. For the cis isomer the following structure has been obtained from nine isotopic species: O=N = 1.182 Å, N-O = 1.398 Å, O-C = 1.437 Å, C-Hi (in-plane) = 1.09 Å, C-H0 (out-of-plane) = 1.102 Å, ∠ONO = 114.8°, ∠NOC = 114.7°, ∠OCHi = 101.8°, ∠OCH0 = 109.9°, and ∠H0CH0 = 108.1°. The methyl group was found to be tilted by ∼5° with the expected conformation. Nitrogen quadrupole coupling constants determined for cis-CD3ONO have allowed the complete field gradient tensor to be obtained. Analysis of isotopic spectra for the trans molecule was complicated by nonrigidity due to the very low methyl barrier. Splittings of the K-1 = 0, m = ±3, μa R-branch transitions gave V3 values of 29 and 46 cal mol-1 for CH3ONO and CD3ONO, respectively (61 and 49 cal mol-1 when V6 is taken into account), considerably lower than that previously reported for CH3ONO. Analysis of spectra for six isotopic species gave the following structural parameters for the trans isomer: O=N = 1.164 Å, N-O = 1.415 Å, O-C = 1.436 Å, ∠ONO = 111.8° and ∠NOC = 109.9°. The structural properties of cis- and trans-methyl nitrite are discussed. © 1979 American Chemical Society.