Substituent effects on the ionization reaction of β-mesylate phenethyl radicals?

Organic & Biomolecular Chemistry Pub Date: 2003-05-08 DOI: 10.1039/B301959D

Abstract

A series of β-methanesulfonate phenethyl radicals bearing a range of electron donating and withdrawing aromatic substituents were generated and studied in a variety of solvent mixtures using nanosecond laser flash photolysis. Rate constants for the formation of the corresponding styrene radical cation via heterolytic loss of the β-mesylate leaving group were measured using time-resolved absorption spectroscopy. The ionization reaction was investigated in a variety of solvents and solvent mixtures including 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,2-trifluoroethanol, acetonitrile, methanol and water. The influence of substituent electronic effect and solvent polarity on the kinetics of the β-heterolysis reaction are discussed and assessed using the σ+ Hammett parameter and YOMs values, respectively. The small magnitude of m calculated for the formation of the 4-methoxystyrene radical cation by ionization of the mesylate group (m = 0.33) in aqueous methanol mixtures is compared to values obtained for the formation of the same radical cation via loss of chloride and bromide where m = 0.56 and m = 0.45, respectively.

Graphical abstract: Substituent effects on the ionization reaction of β-mesylate phenethyl radicals
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