22673-58-1Relevant academic research and scientific papers
Effect of medium on the rate constant of decarbonylation of phenylacetyl radical
Tsentalovich,Kurnysheva,Gritsan
, p. 237 - 240 (2007/10/03)
The rate constant kCO of decarbonylation of phenylacetyl radicals generated by photolysis of dibenzyl ketone was measured by laser flash photolysis technique in six solvents in a wide temperature range. The pre-exponential factors A and activation energies Ea of decarbonylation were found for all solvents. The kCO value decreases with an increase in the dielectric constant ε of the solvent, whereas an increase in the ability of the solvent for hydrogen bonding increases kCO. The results of quantum-chemical calculations confirm the mutual compensation of the contributions of specific and nonspecific solvations to the activation energy of decarbonylation in alcohols.
A comparative study of magnetic field effects on the dynamics of geminate and random radical pair processes in micelles
Cozens, Frances L.,Scaiano
, p. 5204 - 5211 (2007/10/02)
Magnetic field effects on the dynamics of random radical-radical reactions in micellar systems are reported for the self-reaction of benzyl radicals in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) micelles. The self-reaction rate constants (2k1) determined using laser flash photolysis techniques are reduced by 44% (SDS) and 35% (CTAC) by application of moderate fields. One-half of the maximum magnetic field effect can be achieved with as little as 200 and 120 G in SDS and CTAC micelles, respectively. The results are discussed in terms of a single kinetic model where 75% of random encounters lead to micellized triplet radical pairs where micellar escape and intersystem crossing are competitive processes. The implications of these observations in biological chemistry are briefly discussed. The benzyl radicals were produced from dibenzyl ketone. In short time scales the geminate radical pairs involve benzyl and phenylacetyl radical pairs. The dynamics of this widely studied system were examined in detail. For example, for the SDS system, it is estimated that phenylacetyl exit occurs with a rate constant of ～6.6 × 106 s-1 (compared with 1.4 × 106 s-1 reported for benzyl), and geminate reaction with Kgem = 1.2 × 107 s-1. Of the initial benzyl-phenylacetyl geminate radical pairs, approximately 23% decarbonylate, 31 % separate, and 46% undergo geminate reaction.
Primary Processes in the Type I Photocleavage of Dibenzyl Ketones. A Pulsed Laser and Photochemically Induced Dynamic Nuclear Polarization Study
Gould, Ian R.,Baretz, Bruce H.,Turro, Nicholas J.
, p. 925 - 929 (2007/10/02)
The primary homolytic α-cleavage, and subsequent decarbonylation of the intermediate phenacyl radicals, have been studied for the type I photoreaction of a series of dibenzyl ketones, using the techiques of pulsed laser photolysis and photochemically induced dynamic nuclear polarization (photo-CIDNP).Evidence for selective primary cleavage to produce the most stable radical pairs is obtained for unsymmetrical ketones.The absolute rate constants and activation parameters for the decarboxylations are obtained, and the relationships between these and the stabilities of the product radicals is discussed.
Flash photolysis of phenylacetatopentaminecobalt(III) in aqueous solution. Generation of benzyl radicals and their reversible trapping by cupric ions in homogeneous and micellar solutions
Scaiano, J. C.,Leigh, W. J.
, p. 2355 - 2358 (2007/10/02)
The photodecomposition of (ClO4)2 is a convenient source of benzyl radicals in aqueous systems.The radicals react with cupric ions with a rate constant of (2.1 +/- 0.2)E-7 M-1 s-1 to yield a complex that is formed reversibly.This complex can decay to Cu(I), but at high radical concentrations the recombination of benzyl radicals in equilibrium with it can become the predominant decay path.The reaction of benzyl radicals (from 1,3-diphenylacetone) in anionic micelles in the presence of Cu2+ leads to strong signals from the same intermediate, CuCH2C6H52+.
Absolute Rate Constants for the Decarbonylation of the Phenylacetyl Radical
Lunazzi, L.,Ingold, K. U.,Scalano, J. C.
, p. 529 - 530 (2007/10/02)
The rate of α scission of the phenylacetyl radical has been determined by laser flash photolysis in isooctane, methanol and tetrahydrofuran.There is no significant solvent effect on the rate.In isooctane, the rate constant for decarbonylation can be represented by log (k/s-1) = (12.0 +/- 0.3) - (6.9 +/- 0.4)/2.3RT kcal/mol.
Absolute Rate Constants for Decarbonylation of Phenylacetyl and Related Radicals
Turro, Nicholas J.,Gould, Ian R.,Baretz, Bruce H.
, p. 531 - 532 (2007/10/02)
The rate constants and Arrhenius parameters for decarbonylation of phenylacetyl (C6H5CH2CO), phenylmethylacetyl (C6H5CHCH3CO), and phenyldimethylacetyl radicals in isooctane have been determined by laser flash photolysis.The variation of the rate constant for decarbonylation follows the pattern expected from radical stabilities, but the activation energies do not.It is proposed that previously unrecognized conformational restrictions may be significant in determinig decarbonylation rates.
MEASUREMENT OF RATE PROCESSES OF FREE RADICALS IN HOMOGENEOUS AND MICELLAR SOLUTIONS BY CIDNP
Lehr, Gary F.,Turro, Nicholas J.
, p. 3411 - 3420 (2007/10/02)
CIDNP is used to study rate processes of free radicals in both homogeneous and micellar solutions.An estimate of the lifetime of the phenyl-acetyl radical at ambient temperature (τ-CO>/=1E-7sec) produced during photolysis of dibenzyl ketone is made based on quantitative CIDNP measurements and computer simulations.Observation of CIDNP in micellar solution is shown to be consistent with an isotropic medium which restricts diffusion on a short time scale, allowing for an increased tendency toward cage reaction.In the case of t-butyl/pivaloyl radical pairs, escape of the radical fragments from the micelle is shown to be competitive with decarbonylation of the pivaloyl radical.Likewise, CIDNP is consistent with product yield results which show the enhanced tendency of triplet born benzyl radical pairs to undergo cage reaction when they are sequestered in a micelle.
LASER-PHOTOLYSIS STUDY OF THE EXTERNAL MAGNETIC FIELD EFFECT UPON THE PHOTODECOMPOSITION REACTION OF 1,3-DIPHENYL-2-PROPANONE IN A MICELLE
Hayashi, Hisaharu,Sakaguchi, Yoshio,Nagakura, Saburo
, p. 1149 - 1152 (2007/10/02)
The photodecomposition reaction of 1,3-diphenyl-2-propanone in a micelle was studied with the aid of ns laser-photolysis.The transient absorption due to the benzyl radical was observed and the amount of escaping benzyl radicals from radical pairs was found to be enhanced by 30percent in the presence of a magnetic field of 70 mT.
