Evaluation of theoretical techniques

The theoretical calculations used to study the various mechanistic possibilities are based on ab initio molecular orbital theory. Previous theoretical studies of 

To directly assess the performance of different theoretical techniques, we have chosen to present the barriers (AHt) and reaction enthalpies (AH) at 0 K and to exclude the zero-point vibrational energy. In order to make a meaningful comparison with experiment, the experimental activation energy and enthalpy of reaction must be back-corrected accordingly. We have accomplished these corrections by using zero-point vibrational energies and temperature corrections calculated at the B3-LYP/6-31G(d) level. This leads to an experimental vibrationless AHt at 0 K of 31.2 kj moT [60] and, depending on which experimental value is used [59-61], vibrationless enthalpies of reaction at 0 K (AH) of -6.9 kJ moT, -8.0 kJ mol, -11.6 kJ mol or -19.4 kJ mol are obtained [62]. 

The B3-LYP barriers obtained with three different basis sets are in impressive agreement with experiment, particularly considering the relatively inexpensive 

G2(MP2)-RAD, which implements restricted-open-shell versions of both coupled cluster and perturbation theories. The latter method has been shown to generally yield reliable results when applied to open-shell systems [66]. 

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