Abstract The i.r. spectra of cis and trans 1-nitropropene have been recorded in the vapor phase and in various solvents. Theoretical calculations at the Hartree—Fock level with a 3-21G(d) basis set were carried out yielding vibrational frequencies for nitromethane and cis and trans 1-nitropropene. Assignment of fundamentals was assisted by solvent effects on 1-nitropropene. Evidence is obtained for inter-molecular hydrogen bonding.