Reactivities of triarylmethyl and diarylmethyl cations with azide ion investigated by laser flash photolysis. Diffusion-controlled reactions

1991 ◽  
Vol 113 (3) ◽  
pp. 1009-1014 ◽  
Author(s):  
Robert A. McClelland ◽  
V. M. Kanagasabapathy ◽  
Narinder S. Banait ◽  
Steen Steenken
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Azide Ion ◽  
Diffusion Controlled

Formation and nucleophilic capture of N-nitrosiminium ions

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1148-1161 ◽  
Author(s):  
Latifa Chahoua ◽  
Alain Vigroux ◽  
Yvonne Chiang ◽  
James C Fishbein
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Aqueous Media ◽  
Laser Flash ◽  
Azide Ion ◽  
Iminium Ions ◽  
Nucleophilic Trapping

A study of the solvolysis of a series of (N-nitrosomethylamino)arylmethyl esters and azides and the products of nucleophilic trapping of the corresponding N-nitrosiminium ion intermediates in aqueous media, 25°C, ionic strength 1 M is reported. Structure-reactivity data for the forward and reverse reactions have been obtained. In three cases, the rate constants for reactions of the cations with nucleophiles have been measured directly by laser flash photolysis. The data allow a comparison of the degree to which the N-methyl-N-nitroso functionality enhances cation stability from a thermodynamic and kinetic perspective. It has been possible to deduce that the carbon basicity of azide ion is less than 1 kcal/mol greater than that of acetate ion.Key words: nitrosiminium ions, α-acetoxynitrosamines, carbocations, iminium ions, nucleophilicity.

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

2006 ◽  
Vol 84 (7) ◽  
pp. 934-948 ◽  
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.

Laser flash photolysis investigations of diffusion-controlled reactions in supercritical fluids

1993 ◽  
Vol 97 (21) ◽  
pp. 5618-5623 ◽  
Author(s):  
Christopher B. Roberts ◽  
Jianwei Zhang ◽  
Joan F. Brennecke ◽  
John E. Chateauneuf
Keyword(s):  
Supercritical Fluids ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Diffusion Controlled

scholarly journals Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

2009 ◽  
Vol 9 (2) ◽  
pp. 7681-7706 ◽  
Author(s):  
A. Jammoul ◽  
S. Dumas ◽  
B. D'Anna ◽  
C. George
Keyword(s):  
Triplet State ◽  
Transient Absorption ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Chemical Oxidation ◽  
Absorption Feature ◽  
Halide Anion ◽  
Oceanic Surface ◽  
Diffusion Controlled

Abstract. The interactions between benzophenone triplet state and halide anion species (Cl−, Br− and I−) have been studied by laser flash photolysis (at 355 nm) in aqueous solutions at room temperature. The decay of the triplet state of benzophenone was followed at 525 nm. Triplet lifetime measurements provided rate constants, kq (M−1 s−1), close to diffusion controlled limit for iodide (~8×109 M−1 s−1), somewhat less for bromide (~3×108 M−1 s−1) and much lower for chloride (>106 M−1 s−1). The halide (X−) quenches the triplet state, and a product, having a transient absorption at 355 nm and a lifetime much longer than that of the benzophenone triplet state, is formed. This transient absorption feature matches those of the corresponding radical anion (X2−). We therefore suggest that such reactive quenching can be a photosensitized source of halogen in the atmosphere and represents a driving force for the chemical oxidation of the oceanic surface.

The absolute kinetics for radical addition and electronic energy transfer to [1.1.1]propellane

1998 ◽  
Vol 76 (10) ◽  
pp. 1474-1489 ◽  
Author(s):  
P F McGarry ◽  
J C Scaiano
Keyword(s):  
Free Radicals ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Electronic Energy ◽  
Triplet States ◽  
Quenching Rate ◽  
Electronic Energy Transfer ◽  
Diffusion Controlled

Free radicals react more readily with [1.1.1]propellane, 1, than with styrene. For example Et3Si· reacts with 1 and styrene with rate constants of 6 × 108 M-1 s-1 and 2 × 108 M-1 s-1, respectively. Fluorenone, phenanthrene, triphenylene, benzophenone, and pyrene transfer electronic energy to 1 with rate constants well below the diffusion-controlled limit. For example, triplet benzophenone is quenched by 1 with a bimolecular rate constant of 9.9 × 106 M-1 s-1. A linear dependence of the log of the quenching rate constants, log kq, upon the excited-state energy of the donors is found.Key words: propellane, laser flash photolysis, free radicals, triplet states.

Insights into the effect of ketylimine, aldimine, and vinylene group attachment and regiosubstitution on the fluorescence deactivation of fluorene

2011 ◽  
Vol 89 (2) ◽  
pp. 173-180 ◽  
Author(s):  
Stéphane Dufresne ◽  
Thomas Skalski ◽  
W. G. Skene
Keyword(s):  
Excited State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Singlet Excited State ◽  
Bond Rotation ◽  
Diffusion Controlled ◽  
Fluorene Derivative ◽  
Group Attachment ◽  
A Minor

The spectroscopic and electrochemical properties of a 9-substituted fluorene ketylimine (3) were investigated and compared with those of its vinylene analogue (4) to determine the origins of the quenched fluorescence of these compounds. The predominate mode of singlet excited state deactivation of the heteroatomic fluorene was found to be internal conversion involving bond rotation. Meanwhile, its carbon counterpart was found to undergo deactivation preferentially by intersystem crossing to form its triplet, which was confirmed by laser flash photolysis. Both 3 and 4 quenched the fluorescence of fluorene with diffusion-controlled rate constants, implying that the singlet excited states of 3 and 4 are also quenched by intramolecular photoinduced electron transfer (PET). This deactivation mode was found to be exergonically favorable (–90 kJ/mol for 3 and –81 kJ/mol for 4) according to the Rehm–Weller equation. The position of the heteroatomic bond on the fluorene moiety was further found to influence the singlet excited state deactivation pathway. The 2-substituted regioisomer decayed predominately by intramolecular PET and its fluorescence can be restored by acid protonation. Conversely, the PET mechanism is a minor deactivation mode for the 9-substituted fluorene derivative and its fluorescence can be enhanced by suppressing bond rotational modes, possible at low temperature and potentially in thin films.

Effect of Aggregation on Bacteriochlorin a Triplet-state Formation: A Laser Flash Photolysis Study¶

2002 ◽  
Vol 76 (5) ◽  
pp. 480 ◽  
Author(s):  
Xavier Damoiseau ◽  
Francis Tfibel ◽  
Maryse Hoebeke ◽  
Marie-Pierre Fontaine-Aupart
Keyword(s):  
Triplet State ◽  
State Formation ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash
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