Laser flash photolysis study of the reactions of carbonyl triplets with phenols and photochemistry of p-hydroxypropiophenone

Journal Article · Wed Jul 15 04:00:00 EDT 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00404a029· OSTI ID:6323905

Das, P K; Encinas, M V; Scaiano, J C

The quenching of aromatic carbonyl triplets by phenols is a very fast process for both n,..pi..* and ..pi..,..pi..* states. Representative rate constants for benzophenone triplets in benzene are 1.3 x 10/sup 9/ (phenol) and 8.1 x 10/sup 8/ (m-fluorophenol) M/sup -1/ s/sup -1/, while for p-methoxypropiophenone the values are 4.9 x 10/sup 9/ and 5.0 x 10/sup 9/ M/sup -1/ s/sup -1/ for the same pair of substrates; 18 different phenols were examined. The rate constants are smaller in wet acetonitrile as a result of hydrogen bonding; for example for the benzophenone-phenol system we measured 8.0 x 10/sup 7/ M/sup -1/ s/sup -1/. Isotope effects are larger for p-methoxypropiophenone than for benzophenone: for example in the case of phenol the values of k/sub H//k/sub D/ are 3.9 and 1.2, respectively (in wet acetonitrile). The quenching reaction leads to the efficient, but not quantitative, formation of phenoxy and ketyl radicals, with the only exception of p-nitrophenl where the process involves electronic energy transfer. The temperature dependence of a few representative systems, as well as the quenching by methyl ethers of similar structure, has also been examined. The photochemistry of p-hydroxypropiophenone is characterized by efficient self-quenching involving a head-to-tail hydrogen-transfer reaction.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 6323905
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:14; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AROMATICS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ELECTROMAGNETIC RADIATION
EXPERIMENTAL DATA
HYDROXY COMPOUNDS
INFORMATION
KETONES
LASER RADIATION
MULTIPLETS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHENOLS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADIATIONS
SCINTILLATION QUENCHING
TRIPLETS