INFRARED AND RAMAN-SPECTRA, CONFORMATIONAL-ANALYSIS, BARRIERS TO INTERNAL-ROTATION, VIBRATIONAL ASSIGNMENT, AND ABINITIO CALCULATIONS OF TRANS-1,3-DICHLOROPROPENE

The infrared (3200-50 cm-1) and Raman (3200-10 cm-1) spectra of gaseous and solid trans-1,3-dichloropropene, ClHC-CH(CH2Cl), have been recorded. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization ratios have been measured. The fundamental CH2Cl torsion for the more stable gauche conformer has been observed in the far-infrared spectrum of the gas and has a hybrid contour centered at 84.0 cm-1. The corresponding mode for the cis conformer (allylic chlorine atom oriented cis to the double bond) gives rise to a series of well defined C-type Q branches beginning at 129.8 cm-1 and proceeding to lower frequencies. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been obtained: V1 = -558 +/- 7, V2 = -38 +/- 10, V3 = 637 +/- 9, V4 = 174 +/- 7, V6 = -16 +/- 4 cm-1. This potential function has the gauche rotamer more stable by, 318 +/- 26 cm-1 (909 +/- 74 cal/ mol). The gauche to gauche, gauche to cis, and cis to gauche barriers have been determined to be 397, 957, and 639 cm-1, respectively. From studies of the Raman and infrared spectra of the ps at variable temperatures, the conformational enthalpy difference has been determined to be 342 +/- 36 cm-1 (978 +/- 103 cal/mol). A complete assignment of the vibrational fundamentals is proposed. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing either the 3-21G* or 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.