Microwave spectrum of chloromethyl methyl ether

The microwave spectrum of chloromethyl methyl ether has been studied in the region 12.4–40 GHz. For ³⁵Cl species, a- and c-type transitions have been assigned for the ground state, the first excited state of the chloromethyl torsional mode, and the first excited state of the methyl torsional mode. Assignments were also made for the ground state of ³⁷Cl species. The assigned transitions are due to the gauche conformer. The nuclear quadrupole coupling constants were determined for the ground state of ³⁵Cl and ³⁷Cl species. The observed A-E splittings of the rotational transitions arising from the three vibrational states indicate a strong coupling between the two torsional vibrations. A model calculation based on the Hamiltonian previously used by Butcher and Wilson (J. Chem. Phys.40, 1671 (1964)), was carried out to account for the splittings and the vibrational frequencies of the two torsional modes. The barrier to internal rotation of the methyl group is estimated to be V₃ = 647 ± 17 cm^?1 (1.84 ± 0.05 kcal/mole).