Microwave spectrum and structure of nitromethane

Abstract

The microwave spectra of nitromethane and five isotopic species have been investigated. Ground-state moments of inertia for the m= 0 internal rotation state have been used to derive the following structure: C—N = 1.489 Å, N—O = 1.224 Å, ∠ONO = 125.3° and ∠NCH = 107.2°, Nuclear spin weightings for various |K–m| states, derived using non-rigid group theory, have been confirmed by relative intensity measurements in the microwave spectra. The same theory has been used to explain the unusually large increase (0.060 a.m.u. Ų) in the inertial defect of CD₃NO₂.

The structure and bonding of nitromethane is compared with some related molecules. The structure of the nitro group in nitromethane is shown to fit a series of NO₂ compounds, between NO⁺₂ and NO^–₂, where the parameters vary according to the electronegativity of the attached grouping.