RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, VIBRATIONAL ASSIGNMENT AND AB-INITIO CALCULATIONS OF TRANS-1-CHLORO-2-BUTENE

Raman (3200 to 10 cm-1) and infrared (3200 to 50 cm-1) spectra have be en recorded for the fluid and solid phases of trans-1-chloro-2-butene (crotyl chloride, trans-CH3CH=CHCH2Cl), and a complete vibrational ass ignment is proposed. The fundamental asymmetric torsion for the more s table gauche conformer has been observed in the far infrared spectrum of the gas and has a hybrid contour centered at 82.5 cm 1. The corresp onding mode for the syn conformer (allylic chlorine atom oriented syn to the double bond) gives rise to a series of well defined C-type Q-br anches beginning at 110.7 cm-1 and proceeding to lower frequencies. Fr om these data the potential function governing internal rotation of th e asymmetric top has been determined and the following potential coeff icients have been obtained: V1 = -371 +/- 18, V2 = -103 +/- 9, V3 = 66 2 +/- 30, V4 = 123 +/- 5, V6 = -20 +/- 12 cm-1. This potential functio n has the gauche rotamer more stable by 267 +/- 57 cm-1 (763 +/- 163 c al mol-1). The gauche to gauche, gauche to syn, and syn to gauche barr iers have been determined to be 518, 839, and 572 cm-1, respectively. Similarly, the barrier governing internal rotation of the CH3 group ha s also been determined from the far-infrared spectrum of the gas. All of these data are compared with the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the RHF/3- 21G, RHF/6-31G* and MP2/6-31G* basis sets. Additionally, complete equ ilibrium geometries have been determined for both rotamers. The result s are discussed and compared with the corresponding quantities for som e similar molecules.