Infrared, Raman, and microwave spectra and conformations of dl-bisoxirane

Abstract

The Raman spectra of liquid and solid dl-bisoxirane and the infrared spectra of all three phases have been recorded. The microwave spectrum has been studied in the X- and R-band frequency regions. The vibrational data indicate that the molecule exists as a mixture of at least two conformations in the fluid state. The more stable conformer, which has a trans orientation of the two oxirane rings and persists as the only conformer in the crystalline solid state, has also been observed in the microwave spectrum of the vapor. The rotational constants of the ground vibrational state are (in MHz) A = 10998.186, B = 2340.413, and C = 2126.233. From Stark effect measurements, the dipole moment component μ b (along the symmetry axis) is found to be 3.43 ± 0.01 D. Rotational transitions and the Stark effect for two excited vibrational states have also been measured and analyzed. A second conformer, which is 0.23 ± 0.08 kcal/mole (0.96 ± 0.33 kJ/mole) less stable than the trans conformer in the liquid state, is identified as a near-gauche conformer whose dihedral angle is probably between 40° and 50°. The possibility of an additional conformer is considered, and the structure of dl-bisoxirane is discussed in terms of similar molecules.