Microwave Spectrum, Structure, and Nuclear Quadrupole Coupling Constants of 1-Bromo-1-fluoroethane

Abstract

The microwave spectrum of 1-bromo-1-fluoroethane, CHBrF–CH3 and CHBrF–CH2D (79/81Br), has been studied for the first time from 8 to 41 GHz. A least-squares analysis of the observed a- and b-type transition frequencies gave rotational and centrifugal distortion constants and components of the bromine nuclear quadrupole coupling constant tensor in the principal axes system as follows: A = 8979.428(5) MHz, B = 2883.898(3) MHz, C = 2310.535(3) MHz, ΔJ = 0.74(2) kHz, ΔJK = 2.49(3) kHz, ΔK = 5.3(5) kHz, δJ = 0.146(1) kHz, δK = 2.75(4) kHz, χaa = 493.49(29) MHz, χbb − χcc = −38.89(11) MHz, and ‖χab‖ = 161.8(28) MHz for the CH79BrF–CH3 species; A = 8979.257(5) MHz, B = 2859.072(3) MHz, C = 2294.572(3), ΔJ = 0.76(2) kHz, ΔJK = 2.51(3) kHz, ΔK = 4.5(4) kHz, δJ = 0.145(1) kHz, δK = 2.70(4) kHz, χaa = 412.42(27) MHz, χbb − χcc = −32.56 (11) MHz, and ‖χab‖ = 133.3(3) MHz for the CH81BrF–CH3 species. The structural parameters are calculated from the 24 observed rotational constants, and electronic properties of the carbon–bromine bond in 1-bromo-1-fluoroethane are evaluated from the observed nuclear quadrupole coupling constants. These molecular properties are compared with those of other related molecules. The molecular structure of 1-bromo-1-fluoroethane is found to be very close to that of 1,1-difluoroethane except for the C–Br bond.