Enthalpies of Transition State Structures

Enthalpies formation of transition states structures are evaluated via the difference between the calculated value of the TS structure and the calculated value of the stable radical adduct(s) (adjacent product and reactant where both are a single species) at the corresponding levels of calculation. The calculation of the enthalpies of the transition state structures are all performed with DFT, which has been demonstrated in the previous chapters to be an accurate and reliable method. We have calculated one transition state structure with the G3 method because the DFT calculations failed. Zero-point energies (ZPVEs) and thermal corrections to 298.15 K are from DFT calculations. The calculation of AfH%g for the transition state structure has been 

Identification path BFC =0 — TSBFC DO — Benzofuranjl + CO TSBF-CJDO 

Identification path C C4D0R - TSCJC4DO-R - HC =CHCH=CHCH=0 + H0C(=0)CH=CH2 TSCJC4DO-R  

Thermodynamic properties calculated for the current study are presented in Table 7.5. Enthalpy of formation and entropy values are reported at 298 K, as most experimental data are referenced or available at 298 K. This facilitates the use of these thermodynamic properties and the use of isodesmic reaction set. Entropies and heat capacities are calculated by statistical mechanics using the harmonic-oscillator approximation for vibrations, based on frequencies and moments of inertia of the optimized B3LYP/6-311G(d,p) structures. Torsional frequencies are not included in the contributions to entropy and heat capacities instead, they are replaced with values from a separate analysis on each internal rotor analysis (IR). 

The contributions from translation, external rotation, and vibrations are summarized as TVR in Table 7.5 along with the IR. The frequencies representing internal rotor torsions are not included in TVR. 

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