Extent of charge transfer in the photoreduction of phenyl ketones by alkylbenzenes

Journal Article · Wed Nov 26 00:00:00 EST 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00284a041· OSTI ID:7004365

Wagner, P J; Truman, R J; Puchalski, A E; Wake, R

Rate constants for triplet-state reaction of various ring-substituted benzophenones (BPs), acetophenones (APs), and ..cap alpha..,..cap alpha..,..cap alpha..-trifluoroacetophenones (TFAs) with toluene and p-xylene have been determined by a combination of flash kinetics, steady-state quenching, and quantum yield measurements. The relative amounts of primary and tertiary radicals formed by reaction of the same ketones with p-cymene have also been measured. For all three types of ketones, rate constants correlate well with triplet ketone reduction potentials. The magnitude of the kinetic isotope effects observed with toluene-d/sub 8/ and p-xylene-d/sub 10/ diminishes as the ketones become easier to reduce. All of the ketone triplets react with alkylbenzenes primarily by a charge-transfer mechanism, with the rate-determining step changing from complexation to hydrogen transfer as the ketones become harder to reduce. The least reactive AP triplets probably react significantly via simple hydrogen atom abstraction as well. Those ketones with n,..pi..* lowest triplets (all BPs and some APs) react with p-cymene to give primary/tertiary radical ratios that vary no more than a factor of 2 from the 0.40 value displayed by tert-butoxy radicals; those with ..pi..,..pi..* lowest triplets (TFAs and some APs) give ratios that favor primary radicals and that vary by an order of magnitude with the triplet ketone reduction potential. The variation in cymene product ratios reflects different orientations for attack on cymene by n,..pi..* and ..pi..,..pi..* triplets and differing degrees of partial electron transfer within the exciplexes, which are not tight radical ion pairs.

• Research Organization: Michigan State Univ., East Lansing
• OSTI ID: 7004365
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 108:24
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACETOPHENONE
PHOTOCHEMICAL REACTIONS
REDUCTION
BENZOPHENONE
CYMENE
DEUTERIUM COMPOUNDS
ISOTOPE EFFECTS
FLUORINATED ALIPHATIC HYDROCARBONS
TOLUENE
XYLENE-PARA
CHEMICAL REACTION KINETICS
ELECTRON TRANSFER
EXPERIMENTAL DATA
HYDROGEN TRANSFER
PHOTOCHEMISTRY
QUANTUM EFFICIENCY
RADIATIONLESS DECAY
RADICALS
TRIPLETS
ALKYLATED AROMATICS
AROMATICS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DE-EXCITATION
EFFICIENCY
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
HALOGENATED ALIPHATIC HYDROCARBONS
HYDROCARBONS
HYDROGEN COMPOUNDS
INFORMATION
KETONES
KINETICS
MULTIPLETS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
REACTION KINETICS
XYLENES
400500* - Photochemistry
400201 - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation