Photoreactions of biacetyl, benzophenone, and benzil with electron-rich alkenes

Journal Article · Wed Feb 18 04:00:00 EST 1987 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00238a033· OSTI ID:6948592

Gersdorf, J; Mattay, J; Goerner, H

The rate constants (k/sub q/) for fluorescence and phosphorescence quenching of biacetyl by electron-rich alkenes were measured in acetonitrile solution at room temperature. A weak dependence of log k/sub q/ on the free enthalpy change (..delta..G/sub 2/) for electron transfer in the triplet state in the range 0 < ..delta..G/sub 2/ < 1.0 eV indicates formation of a polar exciplex. The strong enhancement of k/sub q/ for 0 > ..delta..G/sub 2/ > -0.70 eV points to electron-transfer processes in singlet and triplet states. Quenching of the phosphorescence and the T-T absorption of benzophenone reveals larger (smaller) k/sub q/ values in the endergonic (exergonic) region, as compared to the Rehm-Weller correlation. The slope of the plot of log k/sub q/ vs. ..delta..G/sub 2/ is similar to that of biacetyl in the endergonic region. The latter indicates that electron transfer in this instance is not the primary step. For benzil the plot of log k/sub q/ vs ..delta..G/sub 2/ resembles more closely that of biacetyl, pointing to a similar mechanism. In the exergonic region electron transfer is observed for benzil (major process) and benzophenone (minor process) by detection of the radical anion with use of nanosecond laser flash photolysis. The yield and half-life of the radical anion depend on the nature of the electron donor and the ketone, the solvent polarity, and the additives (e.g., LiClO/sub 4/, special salt effect). The solvent effect on the photoproducts (oxetanes) is correlated with the free enthalpies of radical ion pair formation.

• Research Organization: Rheinisch-Westfalische Technische Hochschule Aachen, West Germany
• OSTI ID: 6948592
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:4; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ACETONITRILE
ACETYL RADICALS
ACYL RADICALS
ALKENES
BENZILIC ACID
BENZOPHENONE
CARBOXYLIC ACID SALTS
CARBOXYLIC ACIDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DE-EXCITATION
EFFICIENCY
ELECTRON TRANSFER
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXPERIMENTAL DATA
FLUORESCENCE
HYDROCARBONS
HYDROXY ACIDS
INFORMATION
KETONES
KINETICS
LUMINESCENCE
NITRILES
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHORESCENCE
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHYSICAL PROPERTIES
QUANTUM EFFICIENCY
RADIATIONLESS DECAY
RADICALS
REACTION KINETICS
THERMODYNAMIC PROPERTIES