Steinar Dyngeseth, S. Schei, K. Hagen
May 1, 1984
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Journal
Journal of Molecular Structure
Abstract
Abstract The molecular structure of propionyl chloride, CH 3 CH 2 COCl, has been investigated by gas-phase electron diffraction at nozzle temperatures of 293, 367 and 488 K. Rotational constants from microwave spectroscopy were also included in the analysis. The molecules exist as a mixture of two conformers with the methyl group and the chlorine atom anti (torsion angle ∠φ = 0°) or gauche (∠φ = 120°) to each other and with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ was found to be 0.77(0.10), 0.65(0.13) and 0.53(0.11) at 293, 367 and 488 K, respectively. These values correspond to an energy difference Δ E = E g − E a = 6 (σ = 2) kJ mol −1 and an entropy difference Δ S = 7 (σ = 6) J mol −1 K −1 . The results at 488 K for the distance ( r a ) and angle (∠ α ) parameters, with estimated uncertainties of 2σ, are: r (CH) = 1.123(11) A, r (CO) = 1.181(5) A, r (CC=) = 1.522(13) A, r (CC) = 1.526(15) A, r (CCl) = 1.800(6) A, ∠CCO = 127.1(6)°, ∠CCCl = 112.0(3)°, ∠CCC = 112.3(8)°, ∠φ ( gauche ) = 120.0(7.7)°. A normal coordinate calculation was made by developing a valence force field. Using 29 force constants, the 24 vibrational frequencies were calculated with an average deviation from experimental values of 5 cm −1 .