Low frequency vibrational spectra, barrier to internal rotation, and RHF/STO-3G^* ab initio calculations of 3-bromopropene - Durig, J.R.; Tang, Q.; Little, T.S. (Elsevier)
The far-infrared spectrum of gaseous 3-bromopropene, CH"2CHCH"2Br, has been recorded from 350 to 35 cm^-^1 at a resolution of 0.1 cm^-^1. The fundamental asymmetric torsional frequencies of the more stable gauche (dihedral angle CCCBr = 118.0 +/- 0.2^o) and higher energy cis (bromine atom eclipsing the double bond and dihedral angle CCCBr = 0^o) conformers have been observed at about 93 and 113.3 cm^-^1 in the low frequency Raman and far-infrared spectra of the gas respectively. Three excited state torsional transitions falling to lower frequency have also been observed for the cis conformer. From studies of the Raman spectrum of the gas at variable temperatures, a value of 257 +/- 50 cm^-^1 (735 +/- 143 cal mol^-^1) has been determined for the enthalpy difference between the conformers. From these data the asymmetric torsional potential governing internal rotation about the CC has been determined and the potential coefficients are: V"1 = -293 +/- 18; V"2 = -106 +/- 26; V"3 = 825 +/- 12; V"4 = 85 +/- 13; V"6 = -53 +/- 6 cm^-^1. This potential function gives cis to gauche, gauche to gauche and gauche to cis barriers of 749, 770 and 986 cm^-^1 respectively, and an enthalpy difference between the conformers of 237 +/- 56 cm^-^1 (672 +/- 160 cal mol^-^1). The r"0 structural parameters for the heavy atom skeleton of the gauche conformer have been determined from previously reported microwave rotational constants along with a fixed CBr distance taken from the electron diffraction study. The determined parameters (distances in ngstroms, angles in degrees) are: r(C"1 = C"2) = 1.335 +/- 0.003; r(C"2C"3) = 1.492 +/- 0.002; C"1C"2C"3 = 122.6 +/- 0.1; BrC"3C"2 = 110.1 +/- 0.1; C"1C"2C"3Br = 118.0 +/- 0.2. The asymmetric torsional potential surface, complete equilibrium geometries and vibrational frequencies have been calculated using restricted Hartree-Fock calculations with the STO-3G^* basis set. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.
http://linkinghub.elsevier.com/retrieve/pii/0022-2860(92)85002-X
Keywords: V; U