124605-72-7Relevant academic research and scientific papers
Picosecond kinetic study of the dynamics for photoinduced homolysis and heterolysis in diphenylmethyl chloride
Lipson, Matthew,Deniz, Ashok A.,Peters, Kevin S.
, p. 3580 - 3586 (1996)
The kinetics of both the ions and radicals formed upon photolysis of diphenylmethyl chloride, (4-methoxyphenyl)phenylmethyl chloride, and bis(4-methoxyphenyl)methyl chloride in acetonitrile and propionitrile are examined by picosecond pump - probe spectroscopy. Both radical pairs and ion pairs are formed directly from a common excited state. In addition, the geminate radical pair decays by electron transfer to form either the contact ion pair or a covalent bond, as well as undergoes diffusional separation to free radicals.
Dynamics of the transient species generated upon photolysis of diarylmethanes within zeolites - Deprotonation and oxidation reactions
Shea, Suzanne,Schepp, Norman P.,Keirstead, Amy E.,Cozens, Frances L.
, p. 1637 - 1648 (2005)
The oxidation of diarylmethanes is a multistep process involving initial formation of a radical cation, deprotonation of the radical cation to the radical, and oxidation of the radical to the carbocation. The dynamics and efficiency of the last two steps in this process, namely deprotonation and oxidation, in acidic zeolites and non-acid zeolites are examined in the present work as a function of the acidity of the diarylmethane radical cations and the oxidation potential of the diarylmethyl radicals. Our results indicate that rate constants for deprotonation strongly depend on the acidity of the radical cations, but not on the composition of the zeolites. In addition, oxidation of the radicals to the diarylmethyl cations is strongly dependent on both the oxidation potential of the radicals and the oxidizing ability of the zeolite. This dependence allows oxidation potentials of the zeolites to be estimated.
Three-color three-laser photochemistry of di(p-methoxyphenyl)methyl chloride
Hara, Michihiro,Tojo, Sachiko,Majima, Tetsuro
, p. 4778 - 4783 (2003)
Three-color three-laser photochemistry of di(p-methoxyphenyl)methyl chloride ((p-CH3OC6H4)2CHCl = An2CHCl) was studied by three-step excitation using 308-, 355-, and 495-nm lasers with delay times of 100 ns to 3 μs. Di(p-methoxyphenyl)methyl radical (An2CH) was produced together with An2CH in the excited state (An2CH*) and di(p-methoxyphenyl)methyl cation (An2CH+) in quantum yields of 0.09, 0.12, and 0.12, respectively, after a laser flash during 308-nm laser (first laser) photolysis of An2CHCl in acetonitrile. Excitation of An2CH with a 355-nm laser (second laser) resulted in formation of transient absorption of An2CH* and An2CH+ and fluorescence of An2CH* with a peak at 550 nm. The formation of An2CH+ from An2CH requires two-photon energy at 355 nm and proceeds by resonant two-photon ionization (RETPI) of An2CH through sequential excitation of An2CH*. Excitation of An2CH+ with a 495-nm laser (third laser) produced fluorescence with a peak at 560 nm. Although the fluorescence of An2CH+ was also observed without the second laser excitation because of the initial formation of An2CH+ during the first 308-nm laser photolysis, the fluorescence intensity of An2CH+ increased approximately 1.2 times with the second 355-nm laser excitation of An2CH. Therefore, the second laser excitation can perform the conversion of An2CH to An2CH+ through RETPI within the laser flash duration, and the fluorescence intensity of An2CH+ can be controlled by the second irradiation.
Competitive decay pathways of the radical ions formed by photoinduced electron transfer between quinones and 4,4′-dimethoxydiphenylmethane in acetonitrile
Del Giacco, Tiziana,Baciocchi, Enrico,Lanzalunga, Osvaldo,Elisei, Fausto
, p. 3005 - 3013 (2007/10/03)
The reactivity of the cation radical of (4-MeOC6H4)2CH2 photosensitized by 1,4-benzoquinone (BQ), 2,5-dichloro-1,4-benzoquinone (Cl2BQ), and tetrachloro-1,4-benzoquinone (chloranil, CA) was investigated in acetonitrile. The main photoreaction products obtained by steady-state irradiation were identified to be: (4-MeOC6H4)2CHOC6H4OH, sensitized by BQ; (4MeOC6H4)2CHCl, sensitized by Cl2BQ; (4-MeOC6H4)2CHOH, sensitized by CA. The mechanism of their formation was investigated by nanosecond laser flash photolysis that allowed transient species (radical ions, neutral radicals, and ions) to be detected and characterized in terms of absorption spectra, formation quantum yields, and decay rate constants. For all systems, the interaction between the triplet quinone (Q) and (4-MeOC6H4)2CH2 produced the corresponding radical ions (quantum yield φ ≥ 0.72) which mainly decay by back electron transfer processes. Less efficient reaction routes for the radical ions Q.- and (4-MeOC6H4)2CH2.+ were also: i) the proton-transfer process with the formation of the radical (4MeOC6H4)2CH. by use of Cl2BQ; ii) the hydrogen-transfer process with the formation of the cation (4-MeOC6H4)2CH+ in the case of CA. Instead, BQ sensitized a much higher yield of BQH. and (4MeOC6H4)2CH., mainly by the direct interaction of triplet BQ with (4MeOC6H4)2CH2. It was also shown that the presence of salts decreases significantly the rate of the back electron transfer process and enhances the quantum yields of formation of the neutral radicals and ions when Cl2BQ and CA are used, respectively. The behavior of BQ.-, Cl2BQ.-, and CA.- appears to be mainly determined by the Mulliken charges on the oxygen atom obtained from quantum mechanical calculations with the model B3LYP/6-311G(d,p). Spin densities seem to be much less important.
Protonation of Diarylcarbenes by Alcohols: The Importance of Ion Pair Dynamics
Dix, Edward J.,Goodman, Joshua L.
, p. 12609 - 12612 (2007/10/02)
Picosecond laser excitation of either di(p-chlorophenyl)- or di(p-methoxyphenyl)diazomethane generates a transient which we ascribe to the singlet states of di(p-chlorophenyl)- and di(p-methoxyphenyl)carbenes, 1a and 1b, respectively.Picosecond absorption spectroscopy is used to determine their kinetic behavior in various solvents.In the presence of alcohols, these carbenes are protonated, forming contact-ion pairs.These ion pairs partition between collapse to ether products and separation to free carbenium ions, 2a and 2b, which are readily observed.The dynamics of these ion pairs is discussed.Protonation of carbenes can provide an alternative method for the preparation of ion pairs and the investigation of their dynamics.
Proton-transfer reactions of alkylaromatic cation radicals. The effect of α-substituents on the kinetic acidity of p-methoxytoluene cation radicals
Baciocchi,Del Giacco,Elisei
, p. 12290 - 12295 (2007/10/02)
The rates of deprotonation for a number of α-substituted p- methoxytoluene cation radicals (4-MeOPhCH2X·+ with X = H, Me, OAc, OH, OMe, Cl, CN, Ph, 4-MeOPh, and 4-MeOPhCD3·+) have been determined by a laser phot
Photoionization of Diarylmethyl Radicals in Acetonitrile and Alcohol-Water: Laser Flash Production of Diarylcarbenium Ions
Faria, Joaquim L.,Steenken, S.
, p. 1924 - 1930 (2007/10/02)
Diarylmethyl radicals Ar2CH. were produced by 248-nm laser photolysis (20 ns) of diphenylmethane, diphenylmethanol, and diarylmethyl halides in acetonitrile and water:alcohol mixtures.A few microseconds after their generation, the radicals were
Photo-heterolysis and -homolysis of substituted diphenylmethyl halides, acetates, and phenyl ethers in acetonitrile: Characterization of diphenylmethyl cations and radicals generated by 248-nm laser flash photolysis
Bartl,Steenken,Mayr,McClelland
, p. 6918 - 6928 (2007/10/02)
Para-substituted diphenylmethyl halides, acetates, and ethers RPh(R′Ph)CH-X (R, R′ = CF3 to OCH3), upon photolysis with ～250-nm light in acetonitrile solutions, undergo homolysis and heterolysis of the C-X bond to give the radicals, RPh(R′Th)CH? (abbreviated as C?), and the cations, RPh(R′Ph)CH+ (C+). Whereas the quantum yields for homolysis (0.2-0.4) are rather independent of the nature of the substituent on the benzene ring, those for heterolysis increase with increasing electron-donator strength from ≤0.07 for CF3 to 0.3 for OMe. The cation:radical ratios are also dependent on the nucleofugal properties of X. For the halides, the observed heterolysis:homolysis ratios correlate with the pKa values of the conjugate acids HX and not with the electron affinities of X?. In acetonitrile, heterolysis is much less endothermic than homolysis. Homolysis and heterolysis can also be effected indirectly by reaction with triplet acetophenone (produced by 308-nm photolysis). Unless stabilized by one or more MeO, the cations decay predominantly by reaction with acetonitrile to give nitrilium ions. However, since this reaction is reversible (shown for the benzhydryl cation), the nitrilium ion contributes only to an insignificant degree to the formation of the final (cation-derived) products, which result from reaction with trace water (main product, benzhydryl alcohol; minor, benzhydrylacetamide). The rate constants for addition of C+ to CH3CN are in the range 3.5 × 105 to 3.8 × 107 s-1 for the cations with R = R′ = Me to R = H, R′ = CF3. The rate constants for reaction of C+ with halides (ion recombination) are ～2 × 1010 M-1 s-1 (diffusion control). The radicals C? disappear by dimerization and disproportionate, for which a complete mass balance has been achieved by product analysis for the case of the benzhydryl system. At laser-pulse powers > 10 mJ electronically excited radicals, C?*, are additionally formed in many cases, via absorption of a light quantum by ground-state C?.
