Conformational study of ethyl nitrite by microwave spectroscopy

The microwave spectrum of ethyl nitrite shows the presence of three rotational isomers. Two rotamers correspond to text-decoration:underlinecis, trans[τ1(ON—OC)= 0°, τ2(CC—ON)= 180°] and text-decoration:underlinecis, gauche(τ1= 0°, τ2= 80°) structures. Relative intensities show the text-decoration:underlinecis, gauche to be less stable by 238 ± 50 cm–1. A third rotamer, less stable than the text-decoration:underlinecis, trans by 81 ± 20 cm–1, has been assigned a text-decoration:underlinetrans, gauche structure (τ1= 180°, τ2= 90°). Internal rotation about the C—O bond in the text-decoration:underlinecis isomer has been studied through relative intensities of spectra in excited torsional states. For the text-decoration:underlinetrans 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 text-decoration:underlinetrans, gauche CH3CH2ONO and CD3CD2ONO. Dipole moments for the three rotamers are also reported.