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Beilstein J Org Chem. 2013 Apr 24;9:800-8. doi: 10.3762/bjoc.9.91. Print 2013.

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes.

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1
PhotoGreen Lab, Department of Chemistry, University of Pavia, V. Le Taramelli 12, 27100 Pavia, Italy.

Abstract

Steady-state irradiation in neat acetonitrile of some aromatic nitriles, imides and esters (10(-5)-10(-3) M solution) in the presence of tertiary amines allowed the accumulation of the corresponding radical anions, up to quantitative yield for polysubstituted benzenes and partially with naphthalene and anthracene derivatives. The condition for such an accumulation was that the donor radical cation underwent further evolution that precluded back electron transfer and any chemical reaction with the radical anion. In fact, no accumulation occurred with 1,4-diazabicyclo[2.2.2]octane (DABCO), for which this condition is not possible. The radical anions were produced from benzene polyesters too, but decomposition began early. Ipso substitution was one of the paths with secondary amines and the only reaction with tetrabutylstannane. The results fully support the previously proposed mechanism for electron transfer (ET) mediated photochemical alkylation of aromatic acceptors via radical ions and radical intermediates.

KEYWORDS:

aromatic nitriles; persistent radical anion; photochemical activation; photoinduced electron transfer (PET); photooxidant; reactive intermediates

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