The most stable conformer has the //-ethyl group syn to the carbonyl, except for X = H where it is anti to the carbonyl. Activation free energies AG*29s in kcal mol-1 (gas/solution) are 16.4 (0.1)/18.2 (0.1) for X = CF3 (in CCL,), 15.4 (0.2)/18.5 (0.2) for X = CH3 (in DMSO-t/6), and 19.6 (0.2)/21.0 (0.2) for X = H (in DMSO-i/e). Gas-phase values of AG*298 are lower the liquid-phase values by 1.4-3.1 kcal mol-1. This is consistent with previous experimental studies.
Temperature-dependent Berry pseudorotation rate constants of SF4 gas at ca. 7.9 atm, determined from analysis
of exchange-broadened 19F NMR spectra, are consistent with E
∞ = 11.9(0.2) kcal mol-1, A
∞ = 3.56(1.09) ×
1012 s-1, ΔG
⧧
298 = 12.2(0.1) kcal mol-1, ΔH
⧧
298 = 11.3(0.4) kcal mol-1, and ΔS
⧧
298 = −3.3(0.4) cal mol-1
K-1. Using a 6-31+G* basis set, HF calculations predict ΔH
⧧
298 = 12.26 kcal mol-1 and ΔS
⧧
298 = −3.74 cal
mol-1 K-1 and MP2 calculations predict ΔH
⧧
298 = 9.99 kcal mol-1 and ΔS
⧧
298 = −3.89 cal mol-1 K-1.
Stationary point MP4/6-31+G*//HF/6-31+G* calculations predict ΔH
⧧
298 = 11.55 kcal mol-1 and ΔS
⧧
298 =
−3.91 cal mol-1 K-1. DFT calculations using the 6-31+G* basis set and the B3LYP and B3PW91 hybrid
functionals are considerably less accurate. Pressure-dependent rate constants obtained at 335 K agree well
with RRKM theory predictions using the strong collision assumption. The curvature and displacement of the
experimental falloff curve are not significantly perturbed by effects of weak collisions and/or nonstatistical
intramolecular vibrational energy redistribution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.