Absolute Rate Constants for Atomic Fluorine in Solution: Characterization of Reaction Intermediates in the Laser Flash Photolysis of Xenon Difluoride

Absolute rate constants for HO2 + NO and NH2 + NO reactions were measured by a photoionization mass spectrometry coupled with a laser flash photolysis. HO2 and NH2 radicals were photoionized by an Ar resonance lamp and were detected as their parent ions (HO2+ and NH2+). The rate constants were determined to be K(HO2 + NO)=(6.5 ± 2.0) 10−12cm3molecule−1s−1K(NH2 + NO)=(1.9 ± 0.3) 10−11cm3molecule−1s−1 Both rates are consistent with those previously reported.

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Direct detection of methylphenylgermylene and 1,2-dimethyl-1,2-diphenyldigermene — Kinetic studies of their reactivities in solution

Canadian Journal of Chemistry ◽

10.1139/v06-107 ◽

2006 ◽

Vol 84 (7) ◽

pp. 934-948 ◽

Cited By ~ 13

Author(s):

William J Leigh ◽

Ileana G Dumbrava ◽

Farahnaz Lollmahomed

Keyword(s):

Acetic Acid ◽

Rate Constants ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Direct Detection ◽

Kinetic Studies ◽

Laser Flash ◽

Absolute Rate ◽

Hydrocarbon Solvents ◽

Diffusion Controlled

Photolysis of 1,3,4-trimethyl-1-phenylgermacyclopent-3-ene (5) in hydrocarbon solvents containing isoprene, methanol, or acetic acid affords 2,3-dimethyl-1,3-butadiene (DMB) and the expected trapping products of methyl phenylgermylene (GeMePh) in chemical yields exceeding 90%. The germylene has been detected in hexane solution by laser flash photolysis as a short-lived species (τ ~ 2 µs) exhibiting a UV-vis absorption spectrum centered at λmax = 490 nm. It decays with second-order kinetics and a rate constant close to the diffusion-controlled limit, with the concomitant growth of a second longer-lived transient (λmax = 420 nm) that is assigned to a mixture of (E)- and (Z)-1,2-dimethyl-1,2-diphenyldigermene (4). Absolute rate constants have been determined for the reactions of the germylene with primary and tertiary amines (n-BuNH2 and Et3N, respectively), acetic acid (AcOH), a terminal alkyne and alkene, isoprene, DMB, CCl4, and the group 14 hydrides Et3SiH and Bu3SnH. GeMePh is slightly more reactive than GePh2 towards all the reagents studied in this work; both are significantly less reactive than GeMe2 toward the same substrates. Absolute rate constants for the reactions of 4 have also been measured or assigned upper limits in every case and are compared to previously reported values for tetraphenyl- and tetramethyl-digermene with the same reagents.Key words: germylene, digermene, kinetics, laser flash photolysis, germirane, germirene, vinylgermirane, complex, UV–vis spectrum, insertion, addition.

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Reversible Intramolecular Hydrogen Transfer between Cysteine Thiyl Radicals and Glycine and Alanine in Model Peptides: Absolute Rate Constants Derived from Pulse Radiolysis and Laser Flash Photolysis

The Journal of Physical Chemistry B ◽

10.1021/jp805133u ◽

2008 ◽

Vol 112 (47) ◽

pp. 15034-15044 ◽

Cited By ~ 53

Author(s):

Thomas Nauser ◽

Giulio Casi ◽

Willem H. Koppenol ◽

Christian Schöneich

Keyword(s):

Rate Constants ◽

Pulse Radiolysis ◽

Hydrogen Transfer ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Laser Flash ◽

Absolute Rate ◽

Thiyl Radicals ◽

Intramolecular Hydrogen ◽

Model Peptides

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Electrophilicity of a 9-aryl-9-fluorenyl cation in water — Kinetic evidence for antiaromaticity

Canadian Journal of Chemistry ◽

10.1139/v10-032 ◽

2010 ◽

Vol 88 (6) ◽

pp. 493-499 ◽

Cited By ~ 6

Author(s):

Sarah Ward ◽

Tammy Messier ◽

Matthew Lukeman

Keyword(s):

Rate Constants ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Laser Flash ◽

Nucleophilic Attack ◽

Rate Data ◽

Anionic Nucleophiles ◽

Long Lifetime

The 9-(4-methoxyphenyl)-9-fluorenyl cation (2) has been generated in 100% water by laser flash photolysis of 9-(4-methoxyphenyl)-9-fluorenol (3), representing the first observation of a 9-fluorenyl cation in this solvent with lifetimes in the microsecond timescale. The relatively long lifetime permitted quenching studies with a number of anionic nucleophiles, and bimolecular rate constants for each were determined. For both bromide and iodide, rate data suggest that an equilibrium between the cation and trapped product is rapidly established, followed by slower, irreversible trapping of the cation by water. The bimolecular rate constants obtained show that the generated 9-fluorenyl cation is significantly more reactive towards nucleophilic attack, by two orders of magnitude, than related triarylmethyl cations that lack the 4n π-system, lending support to the characterization of fluorenyl cations as antiaromatic.

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