Jr. Durig et al., RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, VIBRATIONAL ASSIGNMENT, AND AB-INITIO CALCULATION OF CIS-1,3-DICHLOROPROPENE, Canadian journal of chemistry, 71(10), 1993, pp. 1751-1763
The Raman (3200-10 cm-1) and infrared (3200-20 cm-1) spectra of gaseou
s and solid cis-1,3-dichloropropene, cis-ClHC=CHCH2Cl, have been recor
ded. Additionally, the Raman spectrum of the liquid with qualitative d
epolarization data has also been obtained. These spectral data have be
en interpreted on the basis that the molecule exists predominantly in
the gauche (allylic chlorine atom oriented gauche to the double bond)
conformation in all physical phases. Some bands in the infrared spectr
um of the gas could be due to a second higher energy conformer but the
lack of corresponding Raman bands casts doubt on such an assignment.
Ab initio Hartree-Fock gradient calculations employing the RHF/6-31G
basis set are consistent with two minima that correspond to the two eq
uivalent gauche forms for the potential surface for the internal rotat
ion about the C-C bond. These minima occur at dihedral angles, less th
an with right parenthesis through(dih) ClCCC, of 122-degrees and 238-d
egrees (0-degrees corresponds to the syn conformation) and the gauche
to gauche barrier at the 180-degrees transition state, which correspon
ds to the anti structure, is 342 cm-1. The barrier from the gauche min
ima to the syn (0-degrees) structure, which is also a transition state
, is 2425 cm-1. Complete equilibrium geometries for the gauche structu
re have been determined with the RHF/3-21G, RHF/6-31G*, and MP2/6-31G
basis sets. A normal coordinate analysis utilizing a harmonic force
field calculation with the RHF/3-21G basis set has been carried out f
or the gauche conformer. The results are discussed and compared with t
he corresponding quantities obtained for some similar molecules.