Barrier Studies in the Halopropenes. I. The Microwave Spectrum, Barrier to Internal Rotation, Quadrupole Coupling Constants, and Microwave Double-Resonance Spectra of 2-Chloropropene

Abstract

The microwave spectra of CH3C35Cl:CH2 and CH3C37Cl:CH2 have been observed in the ground and first excited torsional states. The ground-state rotational constants of CH3C35Cl:CH2 are A=9272.79±0.10 Mc/sec, B=4983.84±0.10 Mc/sec, and C=3304.39±0.10 Mc/sec. The ground-state rotational constants for CH3C37Cl:CH2 are A=9272.31±0.10 Mc/sec, B=4850.48±0.10 Mc/sec, and C=3245.11±0.10 Mc/sec. The quadrupole coupling constants along the appropriate principal inertial axes in the ground torsional state of CH3C35Cl:CH2 are χaa=−68.15±0.10 Mc/sec, χbb=37.11±0.10 Mc/sec, and χcc=31.04±0.10 Mc/sec. The quadrupole coupling constants for CH3C35Cl:CH2 in the excited torsional state were within the experimental error of the corresponding ground-state values. The quadrupole coupling constants in CH3C37Cl:CH2 are χaa=−53.80±0.10 Mc/sec, χbb=29.30±0.10 Mc/sec, and χcc=24.50±0.10 Mc/sec. Analysis of the first excited-torsional-state rotational spectrum yielded a barrier to the internal rotation of the methyl group of 2671±20 cal/mole. Microwave double-resonance experiments were used to provide a positive confirmation for the assignments of the 000→101 and 101→202 transitions in CH3C35Cl:CH2 as well as exhibiting some interesting features in the energy levels involved in the transitions. Two types of experiments were performed. The first experiments involved irradiating the quadrupole components in the 000→101 transition while observing the 101→202 transition. The second set of experiments involved irradiating one of the quadrupole components in the 000→101 transition and using a second klystron to observe the entire 000→101 triplet.

Quantum Chemical and Kinetics Study of the Thermal Gas Phase Decomposition of 2-Chloropropene

“…The resulting high-pressure limit rate coefficients k ∞ , pre-exponential factors A ∞ and activation energies E a∞ are listed in Tables and F (Supporting Information). It should be noted that for the channel similar results were obtained when the molecular partition functions were calculated assuming the CH 3 moiety in the 2-chloropropene and TS-propyne as a free rotor (moment of inertia of 3.110 amu Å 2 , in the molecule and 3.2 amu Å 2 in TS-propyne) or a hindered rotor (barrier height of 2.671 kcal mol –1 in the molecule and 2.3 kcal mol –1 in TS-propyne). This is because the ratio between the partition functions of the transition state and the molecule is very close to 1 in both cases.…”

Recent results and future trends in microwave spectroscopy

“…Alternatively, we may assume that the charge distribution at the nucleus concerned is cylindrical and for the chlorine couplings mentioned this gives couplings in the axial direction which are close to those obtained in the bond direction with the first assumption. Similar data for 2-chloropropene 20 have been extended by Good In ethyl chloride 110 the non-zero off-diagonal element in the tensor in the a,b,c-axis system was evaluated from the couplings in the two species CH 3 CH 2 35 Cl and CH 3 CD 2 35 Cl, and this confirmed that the potential near the chlorine nucleus is approximately cylindrically symmetrical about the C-Cl line, although a slight asymmetry, or slight bending of bonds, could not be excluded, or distinguished, with the available precision. In ethyl bromide 112 the off-diagonal term was found from second order quadrupole effects for various species, and the evidence against appreciable bond bending is even stronger.…”

Density functional theory calculations of nuclear quadrupole coupling constants with calibrated17O quadrupole moments

“…The NQCCs can be obtained experimentally from microwave spectroscopy [6][7][8]. Since the introduction of pure NQR spectroscopy by Dehmelt and Kriiger [9] a direct measurement of NQR frequencies is possible, too.…”