Microwave spectra, structures, and nuclear quadrupole coupling constants of bromofluoroethenes: BrFCCH 2, cis-BrHCCHF and trans-BrHCCHF

Abstract

Microwave spectra of the three isomers of bromofluoroethene, BrFCCH 2, cis-BrHCCHF and trans-BrHCCHF ( 79/81Br), have been studied for the first time from 6 to 50 GHz by Stark modulation spectrometer. For cis- and trans-BrHCCHF, the spectra have also been measured by a Fourier-transform microwave spectrometer. The rotational and centrifugal distortion constants and components of the bromine nuclear quadrupole coupling constant tensor in the principal axes system have been determined as follows: A=10,676.347(4), B=3105.4342(14), C=2403.1913(12), χ aa =578.82(20), χ bb − χ cc =−25.82(12), and |χ ab|=54.3(15) MHz for 79BrFCCH 2; A=10,676.307(4), B=3078.4937(14), C=2387.0176(12), χ aa =483.22(13), χ bb − χ cc =−21.36(11), and |χ ab|=47.5(22) MHz for 81BrFCCH 2; A=15,107.028(3), B=2494.8905(12), C=2139.3062(12), χ aa =278.043(13), χ bb − χ cc =259.33(2), and |χ ab|=431.55(5) MHz for cis- 79BrHCCHF; A=15,098.604(14), B=2474.7752(18), C=2124.3305(34), χ aa =233.04(5), χ bb − χ cc =215.81(8), and |χ ab|=360.28(15) MHz for cis- 81BrHCCHF; A=52,547 (assumed), B=1665.2128(5), C=1612.9504(4), χ aa =514.500(11), χ bb − χ cc =59.53(9), and |χ ab|=266.6(65) MHz for trans- 79BrHCCHF; A=52,535 (assumed), B=1652.2533(5), C=1600.7774(4), χ aa =429.896(10), χ bb − χ cc =49.63(9), and |χ ab|=222.8(77) MHz for trans- 81BrHCCHF. The structural parameters of three isomers are calculated from their six observed rotational constants, and their electronic properties of the carbon–bromine bond are evaluated from the observed nuclear quadrupole coupling constants. These molecular properties of three isomers of bromofluoroethene and the related molecules are compared.