Organic Thermochemistry at High ab Initio Levels. 3. A G3 Study of Cyclic Saturated and Unsaturated Hydrocarbons (Including Aromatics)

Abstract

With the purpose of exploring the reliability of the enthalpies of formation calculated using the G3 method, we have examined a series of saturated and unsaturated alicyclic hydrocarbons varying the size and the number of formal double bonds in the molecule. Heats of formation have been calculated at the G3 level through both atomization reactions and bond separation isodesmic reactions, and comparisons with experimental values and with values previously calculated at the G2(MP2) and G2 levels have been made. The quality of the G3-calculated enthalpies of formation using atomization reactions is comparable to that obtained at the G2 level using bond separation reactions, whereas G3 calculations are two to three times faster than G2 calculations.

Pattern of calbindin‐D28k and calretinin immunoreactivity in the brain ofXenopus laevisduring embryonic and larval development

“…The Δ(g, 0 K) values were obtained by deducting the total computed atomization energies D 0 from the experimental enthalpies of formation of isolated atoms. For a molecule A x B y C z , the atomization reaction is shown below13, 14: …”

“…Isodesmic reactions13, 15, 16 refer to reactions in which the bond types and numbers are retained between reactants and products. Errors are significantly decreased to preserve the chemical environment.…”

A G4MP2 theoretical study on the gas phase enthalpies of formation for various polycyclic aromatic hydrocarbons (PAHs) and other C10 through C20 unsaturated hydrocarbons

“…B.01) 6 and employed standard atomization 19 enthalpy approaches for ∆ f H°( g) estimates. [7][8][9][10][11] We have previously shown G4MP2 calculations are 20 expected to yield near chemically accurate (±4.2-8.4 kJ/mol) ∆ f H (g) estimates, 12,13 consistent with 21 the thermochemical accuracy obtained at the more expensive Gaussian-4 (G4) level. [9][10][11][14][15][16] All 22 final structures were confirmed as true minima on their respective potential energy surfaces and 23 are absent any imaginary frequencies.…”

The thermochemistry of alkanethiols and thioethers. Estimation of the enthalpies of formation of 1,3-dithiapropane and 1,3,5-trithiapentane

“…This method has been detailed in previous studies. 32,33 The bond separation reactions for 1,3-dithiapropane and 1,3,5-trithiapentane are, respectively:…”