Gas-Phase Nuclear Magnetic Resonance Study of Berry Pseudorotation of SF4. Comparison of Experimental and Calculated Kinetic Parameters and Falloff Kinetics

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 104; no. 15; pp. 3341 - 3348
• Main Authors: Taha, Angela N, True, Nancy S, LeMaster, Clifford B, LeMaster, Carole L, Neugebauer-Crawford, Susan M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 20.04.2000
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp993991f

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.