A theoretical study on bond dissociation energies and oxidation potentials of monolignols

2004 ◽  
Vol 712 (1-3) ◽  
pp. 197-205 ◽  
Author(s):  
Kai Wei ◽  
Shi-Wei Luo ◽  
Yao Fu ◽  
Lei Liu ◽  
Qing-Xiang Guo
Keyword(s):  
Theoretical Study ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Oxidation Potentials

A Theoretical Study of the Effects of Protonation and Deprotonation on Bond Dissociation Energies

1995 ◽  
Vol 117 (34) ◽  
pp. 8816-8822 ◽  
Author(s):  
Susan L. Boyd ◽  
Russell J. Boyd ◽  
Paul W. Bessonette ◽  
Denise I. Kerdraon ◽  
Nicole T. Aucoin
Keyword(s):  
Theoretical Study ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies

Acidities and homolytic bond dissociation energies of the αC—H bonds in ketones in DMSO

1990 ◽  
Vol 68 (10) ◽  
pp. 1714-1718 ◽  
Author(s):  
Frederick G. Bordwell ◽  
John A. Harrelson Jr
Keyword(s):  
Gas Phase ◽  
Radical Cations ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Oxidation Potentials ◽  
Stabilization Energies ◽  
Conjugate Bases

Equilibrium acidities in DMSO are reported for nine cycloalkanones, acetone, acetophenone, and 19 of their α-substituted derivatives. Oxidation potentials in DMSO for the conjugate bases of most of these ketones are also reported. Combination of these EOX(A−) and pKHA values gives estimates of the homolytic bond dissociation energies (BDEs) of the acidic C—H bonds in the ketones. The ΔBDEs, relative to the BDE of CH3-H, or a parent ketone, provide a measure of the radical stabilization energies (RSEs) of the corresponding radicals. The effects of successive α-Me and α-Ph substitutions on RSEs, relative to those of CH3COCH2-H or PhCOCH2-H, are similar to those reported in the gas phase for methane. The RSE for the MeĊHCOPh radical, relative to CH3• is 17 kcal/mol, which is smaller than the sum of the RSEs of the MeCH2• and PhCOCH2• radicals relative to CH3• (7 + 12 = 19), contrary to the prediction of the captodative postulate. When G in PhCOCH2G is PhCO, CH3CO, or CN the ΔBDEs (relative to PhCOCH2-H) are 0, 1, and 3 respectively; for MeCOCH2SO2Ph, PhCOCH2SO2Ph, and PhCOCH2NMe3+ the ΔBDEs are −5, −2, and −4, respectively. The BDEs in C5, C6, C7, C8, C10, and C12 cycloalkanones are within ±2.5 kcal/mol of that of 3-pentanone. Acetophenones bearing meta or para substituents all have BDEs of 93-94 kcal/mol. Ketone radical cations, [RCOR′]+•, appear to be superacids with estimated [Formula: see text] values below −25. Keywords: acidities, bond dissociation energies, ketones.

A theoretical study of conformational deuterium isotope effects and bond dissociation energies of diastereotopic hydrogens

1991 ◽  
Vol 69 (9) ◽  
pp. 1408-1412 ◽  
Author(s):  
Saul Wolfe ◽  
Chan-Kyung Kim
Keyword(s):  
Theoretical Study ◽  
Isotope Effects ◽  
Model Systems ◽  
Bond Dissociation Energies ◽  
Model Compounds ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Deuterium Isotope Effects ◽  
Derivatives Of ◽  
Good Agreement

In the conformations that correspond to the C6-X1-C2-X3-C4 moieties of 1,3-dioxane, 1,3-dithiane, and cyclohexane in their chair conformations, the model systems CH2(OH)2, CH2(SH)2, and gauche-butane contain "axial" and "equatorial" hydrogens. The vibrational frequencies of the diastereomeric monodeuterated CHD derivatives of these model compounds have been computed ab initio at the 6-31G*//6-31G* level of theory, scaled by 0.9, and used to calculate the conformational deuterium isotope effects in these systems, as well as the stretching and bending components of these isotope effects. The results are in very good agreement with the experimental observations and with some of the interpretations given by Anet for the six-membered rings. Using an equation suggested by McKean, the scaled isolated stretching frequencies have been used to predict the bond dissociation energies of the diastereotopic hydrogens of these molecules. The results suggest that the preference for radical abstraction of the axial C2 hydrogen in a 1,3-dioxane will be diminished in cyclohexane, and reversed in a 1,3-dithiane. Key words: stereochemistry, isotope effects, bond dissociation energies.

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