Conformational study of ethyl nitrite by microwave spectroscopy

Abstract

The microwave spectrum of ethyl nitrite shows the presence of three rotational isomers. Two rotamers correspond to cis, trans[τ₁(ON—OC)= 0°, τ₂(CC—ON)= 180°] and cis, gauche(τ₁= 0°, τ₂= 80°) structures. Relative intensities show the cis, gauche to be less stable by 238 ± 50 cm^–1. A third rotamer, less stable than the cis, trans by 81 ± 20 cm^–1, has been assigned a trans, gauche structure (τ₁= 180°, τ₂= 90°). Internal rotation about the C—O bond in the cis isomer has been studied through relative intensities of spectra in excited torsional states. For the trans isomer, a precise barrier height of 137 ± 7 cm^–1 separating the two equivalent gauche forms has been derived from vibration–rotation interactions in the v= 1, C—O torsional state spectra of both trans, gauche CH₃CH₂ONO and CD₃CD₂ONO. Dipole moments for the three rotamers are also reported.