CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, VIBRATIONAL ASSIGNMENT, AND ABINITIO CALCULATIONS OF 2-CHLOROPROPENOYL FLUORIDE

The far-infrared spectrum of gaseous 2-chloropropenoyl fluoride, CH 2CClCFO, has been recorded at a resolution of 0.10 cm-1 in the region of 350-35 cm-1. The fundamental asymmetric torsional frequencies of the more stable s-trans (two double bonds oriented trans to one another) and the high energy s-cis conformations have been observed at 67.80 and 49.96 cm-1, respectively, each with several excited states falling to lower frequencies. From these data the asymmetric torsional potential function governing the internal rotation about the C-C bond has been determined. The potential coefficients are V1 = -125±1, V2 = 1586±6, V3 = 375±2, V4 = -36±2, and V5 = -65±1 cm-1. The s-trans to s-cis and s-cis to s-trans barriers have been determined to be 1755 and 1570 cm-1, respectively, with an energy difference between the conformations of 185±9 cm-1 (529±26 cal/mol). From studies of the Raman spectrum at variable temperatures, the conformational enthalpy difference has been determined to be 176±40 cm-1 (503±114 cal/mol) and 625±51 cm-1 (1787±146 cal/mol) for the gas and liquid, respectively. A complete assignment of the vibrational fundamentals observed from the infrared spectra (3500-50 cm-1) of the gas and solid and the Raman spectra (3200-10 cm-1) of all three physical states is proposed. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing both the 3-21G* and 6-31G* basis sets. Additionally, complete equilibrium geometries have been determined for both rotamers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules. © 1990 American Institute of Physics.