Microwave spectrum of nitrocyclopropane

The microwave spectrum of nitrocyclopropane has been investigated in the 8–40‐GHz region. Transitions in the ground state and five excited states of the torsional mode have been assigned. The ground state of a monodeuterated nitrocyclopropane has also been assigned. The conformation of the molecule is found to be the bisected one with the plane of the nitro group perpendicular to the plane of the cyclopropyl ring. The torsional frequency $\text{(70± 20\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}})$ of the nitro group and the barrier to internal rotation $\text{(1100± 500\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}})$ have been derived from relative intensity measurements of transitions in the ground and first torsional states. The dipole moment is found to be $\text{3.95± 0.10\hspace{0.17em}}\mathrm{D}$ .