TY - JOUR

T1 - Electrochemistry of electron-transfer probes. The role of the leaving group in the cleavage of radical anions of α-aryloxyacetophenones

AU - Andersen, Mogens L.

AU - Mathivanan, N.

AU - Wayner, Danial D.M.

PY - 1996/5/22

Y1 - 1996/5/22

N2 - The formal reduction potential (E°) of α-phenoxyacetophenone has been determined from the voltammetric peak potential obtained by linear sweep voltammetry in combination with the rate constant for fragmentation of the radical anion which had been determined by laser flash photolysis. The E° values of a number of α-aryloxyacetophenones were then estimated from a correlation of the 13C chemical shifts of the carbonyl carbon and a similar correlation (E* versus 13C chemical shift) within a series of substituted α-anilinoacetophenones. Using these potentials (which vary by only 34 mV over a wide range of substituents) the rate constants for fragmentation of the α-aryloxyacetophenone radical anions were determined from digital simulation of the corresponding voltammetric waves. The fragmentation rate constants were shown to correlate with the pK(a) of the corresponding phenols. However, the kinetic range was too small and the experimental errors too large to allow a distinction between a linear and quadratic free energy dependence. A thermochemical analogy between the leaving group ability in reactions of radical anions and that in simple heterolysis of closed shell compounds is developed. The utility of these compounds as potential electron transfer probes is discussed.

AB - The formal reduction potential (E°) of α-phenoxyacetophenone has been determined from the voltammetric peak potential obtained by linear sweep voltammetry in combination with the rate constant for fragmentation of the radical anion which had been determined by laser flash photolysis. The E° values of a number of α-aryloxyacetophenones were then estimated from a correlation of the 13C chemical shifts of the carbonyl carbon and a similar correlation (E* versus 13C chemical shift) within a series of substituted α-anilinoacetophenones. Using these potentials (which vary by only 34 mV over a wide range of substituents) the rate constants for fragmentation of the α-aryloxyacetophenone radical anions were determined from digital simulation of the corresponding voltammetric waves. The fragmentation rate constants were shown to correlate with the pK(a) of the corresponding phenols. However, the kinetic range was too small and the experimental errors too large to allow a distinction between a linear and quadratic free energy dependence. A thermochemical analogy between the leaving group ability in reactions of radical anions and that in simple heterolysis of closed shell compounds is developed. The utility of these compounds as potential electron transfer probes is discussed.

UR - http://www.scopus.com/inward/record.url?scp=0029885552&partnerID=8YFLogxK

U2 - 10.1021/ja954093+

DO - 10.1021/ja954093+

M3 - Journal article

AN - SCOPUS:0029885552

VL - 118

SP - 4871

EP - 4879

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 20

ER -