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

Journal Article · Wed Jul 15 00:00:00 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), Vol. 103:14
• Country of Publication: United States
• Language: English

Related Subjects

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