Shortcomings of Basing Radical Stabilization Energies on Bond Dissociation Energies of Alkyl Groups to Hydrogen

2010 ◽  
Vol 75 (16) ◽  
pp. 5697-5700 ◽  
Author(s):  
Andreas A. Zavitsas ◽  
Donald W. Rogers ◽  
Nikita Matsunaga
Keyword(s):  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Alkyl Groups ◽  
Stabilization 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.

Bond Dissociation Energies and Radical Stabilization Energies Associated with Substituted Methyl Radicals

2001 ◽  
Vol 105 (27) ◽  
pp. 6750-6756 ◽  
Author(s):  
David J. Henry ◽  
Christopher J. Parkinson ◽  
Paul M. Mayer ◽  
Leo Radom
Keyword(s):  
Bond Dissociation Energies ◽  
Methyl Radicals ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Stabilization Energies

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

2008 ◽  
Vol 112 (24) ◽  
pp. 5554-5554 ◽  
Author(s):  
Ambili S. Menon ◽  
Geoffrey P. F. Wood ◽  
Damian Moran ◽  
Leo Radom*
Keyword(s):  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Stabilization Energies

C−H Bond Dissociation Energies of Alkyl Amines:  Radical Structures and Stabilization Energies§

1997 ◽  
Vol 119 (38) ◽  
pp. 8925-8932 ◽  
Author(s):  
D. D. M. Wayner ◽  
K. B. Clark ◽  
A. Rauk ◽  
D. Yu ◽  
D. A. Armstrong
Keyword(s):  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Alkyl Amines ◽  
Stabilization Energies

Generalization of an empirical model for bond dissociation energies

1993 ◽  
Vol 71 (4) ◽  
pp. 572-577 ◽  
Author(s):  
Yu-Ran Luo ◽  
Philip D. Pacey
Keyword(s):  
Experimental Data ◽  
Steric Effects ◽  
Bond Dissociation Energies ◽  
Average Deviation ◽  
Ring Strain ◽  
Methyl Substitution ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Alkyl Groups ◽  
Leaving Groups

A relationship between homolytic bond dissociation energies (BDEs) of C—X bonds and the electronegativity of X and the degree of methyl substitution of C has been extended. The range of leaving groups, X, now includes SiH3, GeH3, and PH2 and a variety of C-, N-, and O-centred radicals. Alkyl groups with ethyl and propyl chains attached to the radical centre have been incorporated. Steric effects, including those in bulky silanes, have been treated. The method is believed to be generally applicable where resonance and ring strain are not significant. BDEs for 73 bonds have been calculated; in the 42 cases where experimental data are available, the average deviation is 0.7 kcal/mol.

Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

1987 ◽  
Vol 65 (10) ◽  
pp. 2495-2503 ◽  
Author(s):  
Sándor Fliszár ◽  
Camilla Minichino
Keyword(s):  
Energy Difference ◽  
Approximation Formula ◽  
Bond Dissociation Energies ◽  
Charge Neutralization ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Alkyl Groups ◽  
Symmetric Molecule ◽  
New Energy ◽  
Molecular Ground State

The problem of bond dissociation, R1R2 → R1• + R2•, is addressed from the viewpoint that the fragments, R1 and R2, may not be individually electroneutral in the host molecule, whereas the corresponding radicals certainly are. The mutual charge neutralization of R1 by R2 during the cleavage of the bond linking R1 to R2 is described by an expression featuring only molecular ground-state properties. This expression translates directly into a new energy formula for the dissociation energy, D*(R1R2) = ε(R1R2) + CNE − E*nb + RE(R1) + RE(R2), where both the molecule and the radicals are taken at their potential minimum. The charge neutralization energy, CNE, profoundly affects the relationship between the dissociation (D*) and contributing bond energy (ε), i.e., the energy in the unperturbed molecule. Nonbonded interactions between R1 and R2, E*nb, are almost negligible. The reorganizational energy, RE, measures the energy difference between R• and the corresponding electroneutral group found in the symmetric molecule RR. Numerical applications to alkanes reveal an important cancellation of individual CNE terms accompanying the mutual charge neutralization of alkyl groups during the cleavage of CC bonds, i.e., [Formula: see text]. Theoretical εCC's lead to valid CC bond dissociation energies. In CH bond dissociations, on the other hand, the sum εCH + CNE remains nearly constant although individual εCH's may differ from one another by as much as 6 kcal mol−1. The appropriate approximation, [Formula: see text], shows in what manner charge neutralization energies disguise genuine contributing CH bond energies to create a perception of seemingly constant CH bond contributions.

O - H Bond Dissociation Energies

2011 ◽  
Vol 64 (4) ◽  
pp. 394 ◽  
Author(s):  
Bun Chan ◽  
Michael Morris ◽  
Leo Radom
Keyword(s):  
Density Functional ◽  
Cost Effective ◽  
Closed Shell ◽  
Bond Dissociation Energies ◽  
Functional Theory ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Stabilization Energies ◽  
High Level ◽  
Precursor Molecules

High-level composite, ab initio and density functional theory (DFT) procedures have been employed to study O–H bond dissociation energies (BDEs), as well as radical stabilization energies (RSEs) in the oxygen-centred radicals that are formed in the dissociation of the O–H bonds. Benchmark values are provided by Wn results up to W3.2 and W4.x. We are able to recommend revised BDE values for FO–H (415.6 ± 3 kJ mol–1), MeC(O)O–H (459.8 ± 6 kJ mol–1) and CF3CH2O–H (461.9 ± 6 kJ mol–1) on the basis of high-level calculations. We find that Gn-type procedures are generally reliable and cost-effective, and that some contemporary functionals and double-hybrid DFT procedures also provide adequate O–H BDEs/RSEs. We note that the variations in the O–H BDEs are associated with variations in the stabilities of not only the radicals but also the closed-shell precursor molecules. Most substituents destabilize both species, with σ-electron-withdrawing groups having larger destabilizing effects, while π-electron acceptors are stabilizing. Although there is little correlation between the stabilizing/destabilizing effects of the substituents and the RSEs, we present some general patterns in the RSEs that emerge from the present study.

scholarly journals Estimation of Bond Dissociation Energies and Radical Stabilization Energies by ESR Spectroscopy

1998 ◽  
Vol 63 (6) ◽  
pp. 1935-1943 ◽  
Author(s):  
Jochen J. Brocks ◽  
Hans-Dieter Beckhaus ◽  
Athelstan L. J. Beckwith ◽  
Christoph Rüchardt
Keyword(s):  
Esr Spectroscopy ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Stabilization Energies

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

2007 ◽  
Vol 111 (51) ◽  
pp. 13638-13644 ◽  
Author(s):  
Ambili S. Menon ◽  
Geoffrey P. F. Wood ◽  
Damian Moran ◽  
Leo Radom
Keyword(s):  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Stabilization Energies
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