Stabilization energies and structures of substituted methyl radicals

Pasto, Daniel J.; Krasnansky, R.; Zercher, Charles K.

doi:10.1021/jo00390a019

Cited by 152 publications

(69 citation statements)

References 3 publications

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“…In contrast, eclipsing interactions become more important in longer lived intermediates as a consequence of the slower rate and later transition state, so that more 1,5-trans product is formed. Calculations indicated that the radical stabilization energies of monosubstituted methyl radicals were 2.38 kcal/mol (.CH*OCOH) and 5.30 kcal/mol (.CH20CH3), respectively (26). This order parallels the extent of delocalization of the unpaired electron in related radicals that is reflected by ESR hyperfine splitting constants (27) (RCH20CH2.…”

Section: Resultsmentioning

confidence: 93%

Free-radical based cycloalkanol synthesis and annulation from thioacetal precursors

Yadav¹,

Fallis²

1991

Can. J. Chem.

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A general procedure for the synthesis of diverse cyclopentanols via free-radical cyclization of unsaturated 1,3-oxathiolanes and I ,3-oxathiolan-5-ones is described. The scope of these reactions, including preliminary rate studies that indicate that the 1,3-oxathiolan-5-ones cyclize at a useful rate (I .4 X lo6 M-I S -I at 80°C), has been examined. This permits the rapid assembly, by intramolecular annulation, of various additional ring systems, including bicyclo[3.

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Section: Resultsmentioning

confidence: 93%

Free-radical based cycloalkanol synthesis and annulation from thioacetal precursors

Yadav¹,

Fallis²

1991

Can. J. Chem.

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“…This attenuation is most likely due to the inductive electron withdrawing ability of these substituents; it is known that an electron-withdrawing group usually plays a duel role in radical stability. [100][101][102][103][104][105] A withdrawing group can stabilize a radical by resonance delocalization (π-withdrawing) and at the same time destabilize the radical by electron induction (σ-withdrawing). Destabilization by electron induction is not surprising due to the electron deficient nature of the oxygen radical center, and can be thought of as an unfavorable "pull-pull" dipole-dipole interaction.…”

Section: -95mentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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We have carried out a theoretical study of a series of para-substituted phenoxy radicals in an effort to understand the factors influencing spin and charge density distribution in open-shell systems. The calculations reveal that the distribution of spin and charge are not correlated: cases were found for which spin and charge move together, whereas for other substituents the two quantities exhibit spatially distinct intramolecular polarizations. Charge density variations across the series were found to correlate well with both the Hammett (σ p ) and Hammett-Brown (σ p + ) constants for each substituent, indicating that inductive and/or resonance effects are primarily responsible for the polarization of charge within the molecule. In contrast, the distribution of unpaired spin density could not be adequately accounted for using any of the typical Hammett-type spin delocalization constants cited in the literature. We uncovered an empirical correlation between the polarization of spin density and the R-HOMO-R-LUMO gap of the substituted phenoxy radicals: this led to the development of a simple model based on a three-electron, two-orbital bonding scheme in which mixing between the HOMO of the substituent and the SOMO of the phenoxy moiety serves to define the nature and extent of unpaired spin polarization throughout the molecule. This analysis yielded a correlation coefficient of r > 0.97 for the 15 substituents examined in the study; spin polarization effects in compounds that exhibited the greatest deviation from this correlation could also be readily explained within the context of the model. The underlying reason for the ability to differentially polarize spin and charge likely stems from the fact that net unpaired spin density is completely carried by the unpaired electron (and thus tracks the spatial characteristics of the SOMO), whereas charge density reflects the behavior of all of the electrons of the system. These results could have implications in the field of molecular magnetism, suggesting a means for synthetically tuning the magnitude of intramolecular exchange interactions, as well as providing guidance for the design of catalysts for radical-radical coupling reactions.

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“…This is not so surprising because it is well known that HartreeFock (HF) calculations are not able to correctly predict the energies of the systems when bond breaking and bond making activity is involved [2].…”

Section: Resultsmentioning

confidence: 99%

Calculation of bond dissociation energies for oxygen containing molecules by ab initio and density functional theory methods

Jursic

Martin

1996

Int. J. Quantum Chem.

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rnTwo ab initio (ROHF and MPZ), one local (SVWN), four hybrid (BHandH, BHandHLYP, Becke3LYP, and Becke3P86), and two nonlocal (BLYP and BP86) density functional theory (DFT) methods are used for calculating the dissociation energies of molecules that contain H-0, 0-0 and 0-C bonds. The sensitivity to the basis set of the prediction of bond dissociation energies with DFT methods was tested with Becke3LYP on the H-0 dissociation energy of water. The 6-31 + G(d) methods are chosen as the smallest basis set which produces reasonable results. The calculated values for all other ab initio and DFT methods were performed with these basis sets and then compared with the experimental data. The suitability of DFT methods for computing reliable bond dissociation energies of oxygen containing molecules is discussed.

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Stabilization energies and structures of substituted methyl radicals

Cited by 152 publications

References 3 publications

Free-radical based cycloalkanol synthesis and annulation from thioacetal precursors

Free-radical based cycloalkanol synthesis and annulation from thioacetal precursors

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Calculation of bond dissociation energies for oxygen containing molecules by ab initio and density functional theory methods

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