Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

Abstract

An accurate coupled-cluster (CC) based model chemistry was applied to calculate reliable thermochemical quantities for hydrofluorocarbon derivatives including radicals 1-fluoroethyl (CH-CHF), 1,1-difluoroethyl (CH-CF), 2-fluoroethyl (CHF-CH), 1,2-difluoroethyl (CHF-CHF), 2,2-difluoroethyl (CHF-CH), 2,2,2-trifluoroethyl (CF-CH), 1,2,2,2-tetrafluoroethyl (CF-CHF), and pentafluoroethyl (CF-CF). The model chemistry used contains iterative triple and perturbative quadruple excitations in CC theory, as well as scalar relativistic and diagonal Born-Oppenheimer corrections. To obtain heat of formation values with better than chemical accuracy perturbative quadruple excitations and scalar relativistic corrections were inevitable. Their contributions to the heats of formation steadily increase with the number of fluorine atoms in the radical reaching 10 kJ/mol for CF-CF. When discrepancies were found between the experimental and our values it was always possible to resolve the issue by recalculating the experimental result with currently recommended auxiliary data. For each radical studied here this study delivers the best heat of formation as well as entropy data.

Thermochemistry of Uracil, Thymine, Cytosine, and Adenine

“…The geometries for the single-point CCSD(T) calculations were provided by systematically changing the C−CH 3 torsional angle from 0 to 360°by 15°increments; the resulting structures were partially optimized keeping only the torsional angle fixed and utilizing the MP2/cc-pVTZ level of theory. 38,39 To get an analytical form of the potential, V(ϑ) was expanded in Fourier series…”

“…The one-dimensional Schrödinger equation was solved using the Fourier grid Hamiltonian method. , I r and V (ϑ) are the reduced moment of inertia and the potential obtained from CCSD­(T)/cc-pVTZ calculations, respectively. The geometries for the single-point CCSD­(T) calculations were provided by systematically changing the C–CH 3 torsional angle from 0 to 360° by 15° increments; the resulting structures were partially optimized keeping only the torsional angle fixed and utilizing the MP2/cc-pVTZ level of theory. , To get an analytical form of the potential, V (ϑ) was expanded in Fourier series where V 0 , a n , and b n are fitted parameters. I r was calculated at the equilibrium geometries using Pitzer’s approximation. , …”

High Accuracy Quantum Chemical and Thermochemical Network Data for the Heats of Formation of Fluorinated and Chlorinated Methanes and Ethanes

“…In Table , the results for the diet-HEAT, diet-HEAT-F12, and diet-HEAT-F12-network are shown, along with heats of formation extracted from the literature. A comprehensive collection of literature data and its thorough discussion can be found in our previous works; ,, therefore, data from the current version of the ATcT and JPL databases are shown. Other accurate experimental determinations are listed only if they recommend values different from those of JPL and/or ATcT.…”

“…57 The correction for inversion mode and hindered rotation are adopted from previous works, where it was necessary. 52,56,58 The heats of formation were calculated by using both the atomization and the elemental reaction approach. 52,56 For example, using the atomization reaction, Δ f H T °(CH 3 −CHF) can be calculated as…”

“…Ω is calculated via the standard formulas of statistical thermodynamics within the ideal gas approximation and by using the rigid rotor-harmonic oscillator (RRHO) approximation . The correction for inversion mode and hindered rotation are adopted from previous works, where it was necessary. ,, …”