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Separation of polar and enthalpy effects in radical addition reactions using polar (σ) and radical (σ · ) sigma scales
Author(s) -
Héberger Károly,
Lopata Antal,
Jászberényi J. Cs.
Publication year - 2000
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(200003)13:3<151::aid-poc226>3.0.co;2-0
Subject(s) - chemistry , radical , enthalpy , reactivity (psychology) , nucleophile , hammett equation , polar , electrophile , computational chemistry , photochemistry , medicinal chemistry , reaction rate constant , organic chemistry , thermodynamics , kinetics , catalysis , medicine , physics , alternative medicine , pathology , quantum mechanics , astronomy
Rate constants (k) of radical addition reactions between 15 carbon‐ and sulfur‐centered radicals and 15 vinyl‐type alkenes were collected from the literature. Three descriptor variables {a polar (Hammett) sigma scale [σ(H)] and two radical sigma scales as defined by Creary and co‐workers [σ · (C)] and Dust, Arnold and Wayner [σ · (DAW)]} were chosen to express polar and enthalpy effects. The reactivity data (log k values) of radicals were correlated with the three descriptor variables using stepwise linear regression analysis. The Hammett σ can describe the polar effects, whereas the radical σ · (C) and, to a somewhat lesser extent, σ · (DAW) can describe the enthalpy effects in radical addition reactions. The regression equations support the symmetry pattern of correlations proposed in Part IV. Radical reactivity (log k ) correlates (i) with Hammett σ alone for strongly nucleophilic radicals where polar effects dominate, (ii) with Hammett σ and one of the radical σ · scales for moderately nucleophilic (or electrophilic) radicals and (iii) with one of the radical σ · scales alone for weakly nucleophilic radicals where enthalpy effects dominate. Copyright © 2000 John Wiley & Sons, Ltd.