Organic Thermochemistry at High ab Initio Levels. 1. A G2(MP2) and G2 Study of Cyclic Saturated and Unsaturated Hydrocarbons (Including Aromatics)

Abstract

With the purpose of exploring the reliability of the enthalpies of formation calculated using G2 methods, 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 G2(MP2) and G2 levels through both atomization reactions and bond separation isodesmic reactions, and comparison with experimental values has been made. A linear relationship between the differences between experimental and calculated (from atomization reactions) heats of formation and the number of formal double bonds is obtained.

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:…”

Very High Pressure Single Pulse Shock Tube Studies of Aromatic Species

“…Frequency calculations were performed on the optimized geometries at the same level of theory to confirm that the structures were minima on the potential energy surface and also to obtain the vibrational frequencies and thermal corrections essential for the evaluation of the molecular partition functions. ∆H f 0 298K were extracted from the DFT (B3LYP/6-31G*) energetics using the procedure outlined by Notario et al 43 with the only difference being in the treatment of the vibrations in the calculation of the integrated heat capacity [∆H Vib (T)]. A scaling factor of 0.9989 is applied to the calculated frequencies as recommended by Scott and Radom44 and a low frequency vibrational scaling factor (1.0013) was applied for frequencies less than 625 cm -144 .…”

Gas phase enthalpies of formation, isomerization, and disproportionation of mono- through tetra-substituted tetrahedranes: A G4(MP2)/G4 theoretical study

“…Gas phase (298.15 K, 1 atm) enthalpies of formation (Δ f H°( g) ) were calculated using the atomization approach [38][39][40] (Table 1). Prior work has established that G4MP2/G4 atomization Δ f H°( g) are expected to be at effective chemical accuracy [30,34,35,[41][42][43][44][45][46][47][48].…”