Theoretical Studies on the Thermochemistry of Stable Closed-Shell C1 and C2 Brominated Hydrocarbons

Abstract

The enthalpies of formation of stable closed shell C1 and C2 brominated hydrocarbons have been predicted using Gaussian-3X model chemistry. The entropy, heat capacity, and thermal corrections are calculated from B3LYP/6-31G(2df,p) geometries and vibrational frequencies using rigid-rotor-harmonic-oscillator approximation, except for the quantities of the internal rotations in ethanes, which are calculated using the quantum-mechanical energy levels. Enthalpies of formation have been obtained from G3X atomization and isodesmic reactions. Good agreement is observed on the well-established experimental enthalpies of formation of CH 3Br, CH 2Br 2, CH 2ClBr, and C 2H 3Br from the high-resolution threshold photoelectron photoionization coincidence study.

Unimolecular Reactions of CH2BrCH2Br, CH2BrCH2Cl, and CH2BrCD2Cl: Identification of the Cl−Br Interchange Reaction

“…In some cases supporting calculations were done with the 6-311+G(2d,p) basis set. The calculated moments of inertia and frequencies closely matched the experimental results for C 2 H 5 Br and other calculated results for C 2 H 4 Br 2 . The torsional motion of the CH 2 BrCH 2 Br and CH 2 BrCH 2 Cl molecules is the only unusual aspect of the structures.…”

“…The reliability of the barriers from the calculation for C 2 H 4 BrCl was confirmed by doing a calculation of the potential for C 2 H 4 Br 2 and comparing the result to other calculations. 32,33 Upon the basis of four examples, including that for C 2 H 4 Br 2 , the symmetric-rotor approximation for C 2 H 4 BrCl should be within 15-20% of the density of states using the explicit energy levels of the asymmetric-rotor. 10 In addition to the C 2 H 4 Br 2 and C 2 H 4 BrCl systems, calculations also were done for C 2 H 5 Br as a reference for HBr elimination.…”

Cations of halogenated methanes: adiabatic ionization energies, potential energy surfaces, and ion fragment appearance energies

“…In order to achieve harmony between experiment and theory for this system, sophisticated theoretical calculations may be required to include minor corrections such as relativistic effects, basis set effects, and multireference configuration interactions, etc. On the other hand, the differences on D f H°0 K between G3X and TPEPICO are all within 4 kJ/mol for dihalomethanes [67,85].…”

Thermochemistry of Halomethanes CFnBr4–n (n = 0–3) Based on iPEPICO Experiments and Quantum Chemical Computations

“…Papina et al gave 115.8 ± 3.9 kJ mol –1 , a value disputed by Bickerton et al, who recommended 83.9 ± 3.9 kJ mol –1 . Several computational studies have attempted to tackle this issue: Oren et al arrived at 119.2 kJ mol –1 in a relativistic ab initio study in 2004, Marshall et al used the QCISD(T) method with isodesmic reactions to obtain 110.6 kJ mol –1 , and most recently, Wang obtained 125.4 kJ mol –1 on the basis of the G3X atomization energy (all values at 298 K). The literature values are also summarized in Table .…”

“… a This work, 298 K values for the ions are obtained using the ion convention, i.e., H 298K – H 0K = 0 for the e – . b Based on the Burcat and Csontos values (see text). c Burcat value using the thermal electron convention, the ion convention value being 405.4 kJ mol –1 . d NIST-JANAF compendium e Ruscic et al f Lias et al g See refs − and the text for discussion. h Updated anchor in the thermochemical network. See text for discussion. i Shuman et al j Song et al k Active Thermochemical Tables …”