Pulse radiolysis of 2,4,5-trichlorophenol: formation, kinetics, and properties of hydroxytrichlorocyclohexadienyl, trichlorophenoxyl, and dihydroxytrichlorocyclohexadienyl radicals (original) (raw)
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Ultraviolet absorption spectra and kinetics of CH3S and CH2SH radicals
Chemical Physics Letters, 1991
Acetonyl radicals and acetonylpcroxy radicals were produced by pulse radiolysis of gas mixtures with varying concentrations of CI-I&OCH, and Oz in 1 atm of SF6 to initiate tlte reactions ( 1) F+CI-IsCOCH3-+HFfCH@CH~, (2) ZCH&OCH,-products, (3 ) CHJCOCH2+02( + M)&I-ISCOCH202( + M) and (4) 2CHsCOCHLOL+products. The ultraviolet absorption spectrum of the acetonyl radical is composed of a fairly weak band centered at 3 15 nm and a stronger band in the range of 200-250 nm. The absorption cross section has been determined, a(310 nm)=(8.73~0.50)x10-1g cm* molecule-L. The values k2= (4.8f0.4) x lo-", k,= (1.5+0.3)x lo-'* and k4= (8.3f 1.6) x 10-'zcm3 molecule-' s-' at 298 K were derived by computer modelling of the observed kinetic features. 206 0009-2614/90/$03.50 0 1990 -Elsevier Science Publishers B.V. (North-Holland) volume 173, number 2,3 CHEMICAL PHYSICS LETTERS
Journal of Physical Chemistry A, 2005
The laser-induced fluorescence (LIF) excitation spectra of the 4-methylcyclohexoxy and d11-cyclohexoxy radicals have been measured for the first time. LIF intensity was used as a probe in direct kinetic studies of the reaction of O 2 with trans-4-methylcyclohexoxy and d11-cyclohexoxy radicals from 228 to 301 K. Measured rate constants near room temperature are uniformly higher than the Arrhenius fit to the lower-temperature data, which can be explained by the regeneration of cyclic alkoxy radicals from the product of their-scission and the effect of O 2 concentration on the extent of regeneration. The Arrhenius expressions obtained over more limited ranges were k O 2) (1.4-1 +8) × 10-13 exp[(-810 (400)/T] cm 3 molecule-1 s-1 for trans-4methylcyclohexoxy (228-292 K) and k O 2) (3.7-1 +4) × 10-14 exp)[(-760 (400) /T] cm 3 molecule-1 s-1 for d11-cyclohexoxy (228-267 K) independent of pressure in the range 50-90 Torr. The room-temperature rate constant for the reaction of trans-4-methylcyclohexoxy radical with O 2 (obtained from the Arrhenius fit) is consistent with the commonly recommended value, but the observed activation energy is ∼3 times larger than the recommended value of 0.4 kcal/mol and half the value previously found for the reaction of normal cyclohexoxy radical with O 2 .
The Journal of Chemical Physics, 2013
Irradiation at 193 nm of a p-H 2 matrix containing acryloyl chloride CH 2 CHC(O)Cl at 3.2 K yielded infrared absorption lines at 3143.6 (ν 1), 3057.0 (ν 2), 3048.0 (ν 3), 2103.1 (ν 4), 1461.0 (ν 5), 1349.8 (ν 6), 1223.7 (ν 11 +ν 12 or 2ν 12), 1092.8 (ν 8), 918.1 (ν 9), 691.0 (ν 10), 624.3 (ν 11), and 597.1 (ν 12) cm −1 that are assigned to the 3-propenonyl (•CH 2 CHCO) radical. The assignments are based on the photolytic behavior and a comparison of observed vibrational wavenumbers and infrared intensities with those predicted with the B3PW91/aug-cc-pVDZ method. The observation is consistent with a major radical formation channel CH 2 CHCO + Cl followed by escape of the Cl atom from the original p-H 2 cage. The observation of 3-propenonyl (•CH 2 CHCO) radical but not 3-propenalyl (s-cis-or s-trans-CH 2 CHĊO) radical indicates that the former is the most stable isomer and that the barrier heights for conversion from s-cis-or s-trans-CH 2 CHĊO to •CH 2 CHCO are small.
Nature of the transient species formed in the pulse radiolysis of some thiourea derivatives
Journal of The Chemical Society-perkin Transactions 2, 1994
Reactions of e − aq , OH radicals and H atoms were studied with n-allylthiourea (NATU) using pulse radiolysis. Hydrated electrons reacted with NATU (k = 2.8×10 9 dm 3 mol −1 s −1 ) giving a transient species which did not have any significant absorption above 300 nm. It was found to transfer electrons to methyl viologen. At pH 6.8, the reduction potential of NATU has been determined to be −0.527 V versus NHE. At pH 6.8, OH radicals were found to react with NATU, giving a transient species having absorption maxima at 400-410 nm and continuously increasing absorption below 290 nm. Absorption at 400-410 nm was found to increase with parent concentration, from which the equilibrium constant for dimer radical cation formation has been estimated to be 4.9×10 3 dm 3 mol −1 . H atoms were found to react with NATU with a rate constant of 5 × 10 9 dm 3 mol −1 s −1 , giving a transient species having an absorption maximum at 310 nm, which has been assigned to H-atom addition to the double bond in the allyl group. Acetoneketyl radicals reacted with NATU at acidic pH values and the species formed underwent reaction with parent NATU molecule. Reaction of Cl .− 2 radicals (k = 4.6 × 10 9 dm 3 mol −1 s −1 ) at pH 1 was found to give a transient species with λ max at 400 nm. At the same pH, reaction of OH radicals also gave transient species, having a similar spectrum, but the yield was lower. This showed that OH radicals react with NATU by two mechanisms, viz., one-electron oxidation, as well as addition to the allylic double bond. From the absorbance values at 410 nm, it has been estimated that around 38% of the OH radicals abstract H atoms and the remaining 62% of the OH radicals add to the allylic double bond.
Radical scavenging reactions of chlorogenic acid: A pulse radiolysis study
Research on Chemical Intermediates, 2006
At near neutral pH (approx. 5.5), the OH-adduct of chlorogenic acid (CGA), formed on pulse radiolysis of N 2 O-saturated aqueous CGA solutions (λ max = 400 and 450 nm) with k = 9 × 10 9 dm 3 mol −1 s −1 , rapidly eliminates water (k = 1 × 10 3 s −1) to give a resonance-stabilized phenoxyl type of radical. Oxygen rapidly adds to the OH-adduct of CGA (pH 5.5) to form a peroxyl type of radical (k = 6 × 10 7 dm 3 mol −1 s −1). At pH 10.5, where both the hydroxyl groups of CGA are deprotonated, the rate of reaction of • OH radicals with CGA was essentially the same as at pH 5.5, although there was a marked shift in the absorption maximum to approx. 500 nm. The CGA phenoxyl radical formed with more specific one-electron oxidants, viz., Br • − 2 and N • 3 radicals show an absorption maximum at 385 and 500 nm, k ranging from 1-5.5 × 10 9 dm 3 mol −1 s −1. Reactions of other one-electron oxidants, viz., NO • 2 , NO • and CCl 3 OO • radicals, are also discussed. Repair rates of thymidine, cytidine and guanosine radicals generated pulse radiolytically at pH 9.5 by CGA are in the range of (0.7-3) ×10 9 dm 3 mol −1 s −1 .
The Journal of Chemical Physics, 2012
Irradiation at 239 ± 20 nm of a p-H 2 matrix containing methoxysulfinyl chloride, CH 3 OS(O)Cl, at 3.2 K with filtered light from a medium-pressure mercury lamp produced infrared (IR) absorption lines at 3028.4 (attributable to ν 1 , CH 2 antisymmetric stretching), 2999.5 (ν 2 , CH 3 antisymmetric stretching), 2950.4 (ν 3 , CH 3 symmetric stretching), 1465.2 (ν 4 , CH 2 scissoring), 1452.0 (ν 5 , CH 3 deformation), 1417.8 (ν 6 , CH 3 umbrella), 1165.2 (ν 7 , CH 3 wagging), 1152.1 (ν 8 , S=O stretching mixed with CH 3 rocking), 1147.8 (ν 9 , S=O stretching mixed with CH 3 wagging), 989.7 (ν 10 , C−O stretching), and 714.5 cm −1 (ν 11 , S−O stretching) modes of syn-CH 3 OSO. When CD 3 OS(O)Cl in a p-H 2 matrix was used, lines at 2275.9 (ν 1), 2251.9 (ν 2), 2083.3 (ν 3), 1070.3 (ν 4), 1056.0 (ν 5), 1085.5 (ν 6), 1159.7 (ν 7), 920.1 (ν 8), 889.0 (ν 9), 976.9 (ν 10), and 688.9 (ν 11) cm −1 appeared and are assigned to syn-CD 3 OSO; the mode numbers correspond to those used for syn-CH 3 OSO. The assignments are based on the photolytic behavior and a comparison of observed vibrational wavenumbers, infrared intensities, and deuterium isotopic shifts with those predicted with the B3P86/aug-cc-pVTZ method. Our results extend the previously reported four transient IR absorption bands of gaseous syn-CH 3 OSO near 2991, 2956, 1152, and 994 cm −1 to 11 lines, including those associated with C−O, O−S, and S=O stretching modes. Vibrational wavenumbers of syn-CD 3 OSO are new. These results demonstrate the advantage of a diminished cage effect of solid p-H 2 such that the Cl atom, produced via UV photodissociation of CH 3 OS(O)Cl in situ, might escape from the original cage to yield isolated CH 3 OSO radicals.