Substituent Effects in Radical Chemistry

Viehe, H. G.; Janousek, Z.; Merényi, R.

doi:10.1007/978-94-009-4758-0

Cited by 68 publications

References 6 publications

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An Electronegativity Model for Polar Ground-State Effects on Bond Dissociation Energies

Nau¹

1997

J. Phys. Org. Chem.

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Homolytic bond dissociation energies are a composite of the radical stabilization energies (RSE) of the product radicals and the polar ground-state stabilization energies (PSE) of the reactant molecules. Substituent effects on the PSE are rationalized in terms of changes in the difference of group electronegativities. Thus, the PSE is composed of a bond polarity term, which measures the contribution due to the change in the electronegativity difference between the atoms in the bond, which is broken, and a polar relaxation term, which accounts for the substituent-dependent group electronegativity changes in the remaining bonds. A semi-quantitative model based on Pauling's bonding theory is suitable to assess the direction and relative magnitude of such effects. For the cleavage of benzylic and related bonds, the polar relaxation energy can be neglected (one-bond approximation) to allow the use of correlation analyses and substituent parameters for the interpretation of aryl substituent effects on the PSE. Accordingly, the plots of the PSEs versus substituent parameters should be linear, curved or parabolic depending on the electronegativity difference of the atoms in the bond being broken (⌬EN); moreover, the slopes ( values) should increase linearly with ⌬EN. The predicted dependences of the PSEs on aryl substituents are compared with known experimental results and with the data obtained from semiempirical calculations.

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An Electronegativity Model for Polar Ground-State Effects on Bond Dissociation Energies

Nau¹

1997

J. Phys. Org. Chem.

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Stable Hydrazyls and Push–Pull (Capto‐Dative) Aminyl Free Radicals

Balaban

2017

Patai's Chemistry of Functional Groups

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Electron paramagnetic resonance spectroscopy is at present the preferred method for studying free radicals. Push–pull aminyls show exceptional stability, which is explained satisfactorily by Linnett's double‐quartet theory in terms of electronic spin. Stable hydrazyls such as 2,2‐diphenyl‐1‐picrylhydrazyl and 2,2‐diphenyl‐1‐cyanohydrazyl can actually be viewed as push–pull aminyls. A consequence of Linnett's theory is the increased bond order for the NN bond in hydrazyls, which is confirmed experimentally by X‐ray crystallography and the high intramolecular rotation barrier. For aminyls and hydrazyls whose nitrogen center is not part of a ring, this survey lists the variety of electron donors and electron acceptors known so far.

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Synthetic Utility of the Captodative Effect

Stella¹,

Harvey²

2001

Radicals in Organic Synthesis

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Substituent Effects in Radical Chemistry

Cited by 68 publications

References 6 publications

An Electronegativity Model for Polar Ground-State Effects on Bond Dissociation Energies

An Electronegativity Model for Polar Ground-State Effects on Bond Dissociation Energies

Stable Hydrazyls and Push–Pull (Capto‐Dative) Aminyl Free Radicals

Synthetic Utility of the Captodative Effect

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