Structure and spectra of 1,3,2-dioxaphospholenes. 1. Microwave spectra of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene and its isotopomers in the ground and excited vibrational states

Abstract

The microwave spectrum of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene (1) was studied in the frequency range from 7 to 53 GHz. Rotational transitions of the parent molecule in the ground and eleven excited vibrational states and those of its mono-substituted 37Cl, 13CMe, and 13CCycle isotopomers in the ground vibrational state were identified. Rotational constants and partial rs-structure were obtained. The quartic centrifugal distortion constants, dipole moment components μa = 3.8D and μc = 0.24D (the total dipole moment μ is 3.81D), and the 35Cl quadrupole coupling constants were determined for the parent molecule. The fine structure of the microwave transitions in the parent molecule was analyzed under the assumption of noninteracting methyl groups. The height of the barrier to internal rotation (V30 = V03 = 665 cm–1) and the frequency of torsional vibrations (ν = 167 cm–1) were found. The frequencies of two lowest vibrational modes corresponding to deformation vibrations of the five-membered ring were estimated (ν∼100 cm–1) from the relative intensities of rotational transitions for different vibrational states.