Microwave spectrum, structure, dipole moment and low frequency vibrations of dimethyl cyanamide

Abstract

The microwave spectrum of dimethyl cyanamide has been recorded from 18.0 to 40.0 GHz. Only A-type transitions were observed. The R-branch assignments have been made for the ground state and the first excited state of the skeletal bending mode. It is shown that the heavy atom skeleton is non-planar from the magnitude of the μ c component of the dipole moment as well as from the value of I a+ I b− I c. The following structural parameters were obtained: r(N-CN) = 1.351, ∠CNC = 116°, and an out-of-plane angle of 36° with reasonable assumptions made for the structural parameters for the dimethylamino moiety and the nitrile bond. These parameters are consistent with those previously reported for the cyanamide molecule; they indicate a significant electron delocalization and a large contribution of the sp 2 hybridization on the apex nitrogen. The dipole moment components were determined to be μ a = 4.7 D and μ c = 0.8 D. From the low frequency vibrational data of the solid, a lower limit of 2.5 kcal/mole was obtained for the barrier to internal rotation of the methyl groups.