Chelate ring closure in (o-phenanthroline)pentacarbonylmetal transients (metal = chromium, molybdenum, tungsten) generated by pulsed laser flash photolysis

1991 ◽  
Vol 30 (2) ◽  
pp. 355-356 ◽  
Author(s):  
Shulin. Zhang ◽  
Volker. Zang ◽  
Gerard R. Dobson ◽  
Rudi. Van Eldik
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Chelate Ring ◽  
Pulsed Laser ◽  
Laser Flash ◽  
Ring Closure

Far-UV laser flash photolysis in solution. A time-resolved spectroscopic study of the chemistry of 1,1-dimethyl-1,3-(1-sila)-butadiene

1997 ◽  
Vol 75 (7) ◽  
pp. 975-982 ◽  
Author(s):  
Corinna Kerst ◽  
Martin Byloos ◽  
William J. Leigh
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Activation Parameters ◽  
Laser Flash ◽  
Ring Closure ◽  
Time Resolved ◽  
Decay Rate Constant ◽  
Hydrocarbon Solvents ◽  
First Order Kinetics ◽  
193 Nm

Laser flash photolysis (193 nm) of 1,1-dimethyl-(1-sila)cyclobut-2-ene in hexane solution leads to the formation of a transient species [Formula: see text] assigned to 1,1-dimethyl-1,3-(1-sila)butadiene on the basis of its UV absorption spectrum (λmax = 312 nm), and reactivity toward methanol (kMeOH = (3.6 ± 0.1) × 109 M−1 s−1; kH/kD = 1.3 ± 0.1), ethanol (kEtOH = (2.41 ± 0.06) × 109 M−1 s−1), tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1 s−1; kH/kD = 1.5 ± 0.1), and oxygen [Formula: see text]. Experiments using isooctane and acetonitrile as solvent are also described. In acetonitrile, the lifetime of the silene is shortened considerably compared to hydrocarbon solvents, presumably due to quenching by adventitious water. In isooctane, under conditions of low excitation intensity, the siladiene decays with clean pseudo-first-order kinetics and a maximum lifetime of ~ 5 μs at 23 °C. The decay rate constant varies only slightly with temperature over the 20–60 °C range, leading to Arrhenius activation parameters of Ea = 0.5 ± 0.2 kcal/mol and log A = 5.7 ± 0.2. While steady state irradiation experiments suggest that in the absence of silene traps the predominant fate of the silabutadiene is thermal ring closure to regenerate the precursor, it is concluded that the rate constants and activation parameters for decay of the siladiene measured by flash photolysis represent a composite of those due to thermal electrocyclic ring closure (with Ea > ~3 kcal/mol) and reaction with adventitious quenchers (probably water, with Ea < 0). The measured Arrhenius parameters for reaction of the siladiene with methanol in isooctane (Ea = −2.6 ± 0.3 kcal/mol and log A = 7.6 ± 0.3) are consistent with this proposal. The potential and limitations of the use of 193-nm laser excitation for flash photolysis studies in solution are discussed. Keywords: far-UV, silene, flash photolysis, kinetics, electrocyclic.

Comparison of photoenolization and alcohol release from alkyl-substituted benzoyl benzoic esters

2011 ◽  
Vol 89 (3) ◽  
pp. 331-338 ◽  
Author(s):  
Sivaramakrishnan Muthukrishnan ◽  
Tamara C.S. Pace ◽  
Qian Li ◽  
Brian Seok ◽  
Gerdien de Jong ◽  
...  
Keyword(s):  
Transition State ◽  
Density Functional ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Alkyl Substituent ◽  
Density Functional Theory Calculations ◽  
Laser Flash ◽  
Ring Closure ◽  
Solvent Density ◽  
Transition State Barrier

Photolysis of 1B in argon-saturated solutions yields 4B and releases methanol. Laser flash photolysis of 1B shows formation of biradical 2B, which has a lifetime of ~50 ns and a λmax at 330 nm. Biradical 2B undergoes an intersystem crossing to form photoenols E-3B and Z-3B with a λmax at 390 nm. Laser flash photolysis shows that the lifetimes of E-3B and Z-3B are affected by the solvent. Density functional theory calculations demonstrate that the transition-state barrier for a 1,5-H atom shift from Z-3B to regenerate 1B is affected by the ortho-alkyl substituents, whereas the stereoelectronics of the alkyl substituent affect the transition-state barrier of E-3B as it undergoes electrocyclic ring closure to form 4B. The photoreactivity of 1B was compared with its analogous methyl and isopropyl derivatives 1A and 1C, respectively, to better estimate the effect of the alkyl substituent on reactivity.

scholarly journals Unexpected Reaction Pathway of the Alpha-Aminoalkyl Radical Derived from One-Electron Oxidation of S-Alkylglutathiones

Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 877
Author(s):  
Tomasz Pedzinski ◽  
Krzysztof Bobrowski ◽  
Bronislaw Marciniak ◽  
Piotr Filipiak
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
High Resolution Mass Spectrometry ◽  
Reaction Pathway ◽  
Laser Flash ◽  
Ring Closure ◽  
Unexpected Reaction ◽  
Sulfur Containing ◽  
Resolution Mass ◽  
Intramolecular Ring

Laser flash photolysis and high-resolution mass spectrometry were used to investigate the mechanism of one-electron oxidation of two S-alkylglutathiones using 3-carboxybenzophenone (3CB) as a photosensitizer. This report indicates an unexpected reaction pathway of the α-aminoalkyl radical cation (αN+) derived from the oxidation of S-alkylglutathiones. Instead of a common hydrolysis reaction of αN+ reported earlier for methionine and other sulfur-containing aminoacids and peptides, an intramolecular ring-closure reaction was found for S-alkylglutathiones.

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