Bond Dissociation Energies and Radical Stabilization Energies:  An Assessment of Contemporary Theoretical Procedures

Abstract

Various contemporary theoretical procedures have been tested for their accuracy in predicting the bond dissociation energies (BDEs) and the radical stabilization energies (RSEs) for a test set of 22 monosubstituted methyl radicals. The procedures considered include the high-level W1, W1', CBS-QB3, ROCBS-QB3, G3(MP2)-RAD, and G3X(MP2)-RAD methods, unrestricted and restricted versions of the double-hybrid density functional theory (DFT) procedures B2-PLYP and MPW2-PLYP, and unrestricted and restricted versions of the hybrid DFT procedures BMK and MPWB1K, as well as the unrestricted DFT procedures UM05 and UM05-2X. The high-level composite procedures show very good agreement with experiment and are used to evaluate the performance of the comparatively less expensive DFT procedures. RMPWB1K and both RBMK and UBMK give very promising results for absolute BDEs, while additionally restricted and unrestricted X2-PLYP methods and UM05-2X give excellent RSE values. UM05, UB2-PLYP, UMPW2-PLYP, UM05-2X, and UMPWB1K are among the less well performing methods for BDEs, while UMPWB1K and UM05 perform less well for RSEs. The high-level theoretical results are used to recommend alternative experimental BDEs for propyne, acetaldehyde, and acetic acid.

Photolysis of ortho-nitrobenzylic derivatives: the importance of the leaving group

“…These functionals have proven to perform satisfactorily well in computations of thermodynamic properties of both closed-and open-shell compounds. 35,[43][44][45][46] The resulting enthalpies are given at 0 K (E + scaled ZPVE). All the calculations were performed in gas phase as well as in a polarizable continuum to simulate the solvation effect of the surrounding solvent.…”

“…Note that the radical stabilization energies to be used in this study cannot be replaced by values from tables 35 which usually refer to the methyl radical as a standard, because pairs of substituents can interact, often to different extents in the closed-shell precursors and in the radicals, and thus make that RSEs are not additive. 36 Here, one of the radical substituents is the nitrophenyl moiety, and it is necessary to account for the presence of this substituent in the evaluation of the relative stabilization that additional substituents X provide to radicals 9˙.…”

Bond Dissociation Energies of Organophosphorus Compounds: an Assessment of Contemporary Ab Initio Procedures

“…[27][28][29][30] A study of Hodgson and Coote investigating the relative stabilities of phosphoranyl radicals • P(CH 3 ) 3 X and introducing a new measure of stability, i.e., the α-radical stabilization energy (α-RSE), is of special importance to the present article. 31 As opposed to the standard RSE definition, the α-RSE measures the stability of the radical with respect to P(CH 3 ) 2 X instead of to H-P(CH 3 )X, i.e.…”

On the Reaction of Glycerol Dehydratase with But‐3‐ene‐1,2‐diol

“…This species is expected to enjoy significant stabilization due to the vinyl substituent being adjacent to the radical center. [11] In fact, it is because of this potential stabilization and the associated possibilities for the characterization of hitherto unobserved intermediates and/or unusual functionality that 7 was chosen for investigation as a substrate analogue for Scheme 1. Generally accepted minimal mechanism for the GDH-catalyzed transformation of glycerol (1) into 3-hydroxypropionaldehye (5).…”