Laser Flash Photolysis Studies on the Monohydroxy Derivatives of Benzophenone

1998 ◽  
Vol 102 (20) ◽  
pp. 3470-3480 ◽  
Author(s):  
A. C. Bhasikuttan ◽  
A. K. Singh ◽  
D. K. Palit ◽  
A. V. Sapre ◽  
J. P. Mittal
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Derivatives Of

A Laser Flash Photolysis Study of Some Simple Para-Substituted Derivatives of Singlet Phenyl Nitrene

1999 ◽  
Vol 103 (23) ◽  
pp. 4465-4469 ◽  
Author(s):  
Nina P. Gritsan ◽  
Dean Tigelaar ◽  
Matthew S. Platz
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Derivatives Of

A photochemical retro-Friedel–Crafts alkylation. Rapid rearrangement of cyclohexadienyl cations

1996 ◽  
Vol 74 (12) ◽  
pp. 2518-2527 ◽  
Author(s):  
Earl Macknight ◽  
Robert A. McClelland
Keyword(s):  
Time Scale ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Mechanistic Model ◽  
Laser Flash ◽  
Photochemical Behaviour ◽  
To Come ◽  
Derivatives Of ◽  
Zero Time ◽  
Protonated Cation

This paper reports the use of laser flash photolysis (LFP) techniques to show that cyclohexadienyl cations (σ complexes) of the Friedel–Crafts reaction of 1,3-dimethoxybenzene and the diphenylmethyl cation rearrange on the ns time scale without separating the aromatic compound and the electrophile. This is demonstrated through a study of the photochemical behaviour of 2-diphenylmethyl-1,3-dimethoxybenzene (4) in 1,1,1,3,3,3-hexafIuoroisopropyl alcohol (HFIP). Derivatives of 1,3-dimethoxybenzene have previously been found to selectively protonate at C2 upon excitation in HFIP, and indeed the principal products with 4 are 1,3-dimethoxybenzene (6) and Ph2CHOCH(CF3)2 (7), the species expected if the cyclohexadienyl cation formed in the C2 protonation cleaved Ph2CH+. These products are, however, accompanied by 4-diphenylmethyl- 1,3-dimethoxybenzene (8), a rearranged isomer of 4. A portion of this product is explained by the combination of Ph2CH+ and 1,3-dimethoxybenzene as the latter accumulates during the irradiation. However, 11.5% of 8 is also seen upon extrapolation to zero time. LFP experiments on the ps time scale reveal that the C2 protonated cation, the 1-diphenylmethyl-2,6-dimethoxybenzenium ion (5), is formed within 100–200 ps, and reacts with k = 9 × 108 s−1, with absorbance for Ph2CH+ growing in as 5 decays. LFP studies on the ns time scale reveal that there is a second quantity of Ph2CH+ that grows in, with k = 5.0 × 105 s−1. The precursor for this has been identified as the 1-diphenylmethyl-2,4-dimethoxybenzenium ion (10), the thermodynamically more stable isomer of 5. A mechanistic model is proposed in which excited 4 is C2 protonated in HFIP with k ≥ 1 × 1010 s−1 to form 5, which loses Ph2CH+ with k = 3 × 108 s−1 in competition with rearrangement to 10 with k = 6 x 108 s−1. The cation 10 serves as the second source of Ph2CH+, losing Ph2CH+ with k = 4 × 105 s−1; in competition 10 is deprotonated by HFIP to give 8 with k = 8 × 104 s−1. The 11.5 % of the rearranged 8 that is observed at zero conversion is thus shown to come from an intramolecular pathway in which the key step is the migration of a diphenylmethyl group without separation: 4 → 4* → 5 → 10 → 8. Key words: cyclohexadienyl, photoprotonation, Friedel–Crafts, diphenylmethyl, 1,3-dimethoxybenzene.

scholarly journals Decomposition of S-Nitrosothiols Induced by UV and Sunlight

2009 ◽  
Vol 2009 ◽  
pp. 1-5 ◽  
Author(s):  
Manoj M. Veleeparampil ◽  
Usha K. Aravind ◽  
C. T. Aravindakumar
Keyword(s):  
Photodynamic Therapy ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Major Product ◽  
Quantum Yields ◽  
Induced Decomposition ◽  
Derivatives Of ◽  
Oxidation Of No ◽  
Hplc Analyses

Photochemical release of nitric oxide (NO) from the S-nitroso derivatives of glutathione, L-cysteine, N-acetyl-L-cysteine, L-cysteinemethylester, D,L-penicillamine, N-acetyl-D,L-penicillamine, and N-acetylcysteamine has been investigated at neutral and acidic pH. The release of NO from RSNO is one of the key reactions that could be utilized in photodynamic therapy. The UV-VIS and HPLC analyses have shown that under argon saturated conditions, disulfide (RSSR) is the major product of UV as well as sunlight induced decomposition. While in aerated conditions, nitirite—the end product of the oxidation of NO—was also observed along with disulfide. The formation of thiyl radical as the intermediate was reconfirmed by laser flash photolysis. The initial rate of formation of NO was on the order of 10−10dm3mol−1s−1. The quantum yields of these reactions were in the range of 0.2–0.8. The high quantum yields observed in the photo induced release of NO from RSNO using both UV and sunlight demonstrate the potential application of these reactions in photodynamic therapy.

Laser Flash Photolysis Study of Methyl Derivatives of Phenyl Azide

1999 ◽  
Vol 103 (18) ◽  
pp. 3458-3461 ◽  
Author(s):  
Nina P. Gritsan ◽  
Anna Dóra Gudmundsdóttir ◽  
Dean Tigelaar ◽  
Matthew S. Platz
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Phenyl Azide ◽  
Methyl Derivatives ◽  
Derivatives Of

A Laser Flash Photolysis and Quantum Chemical Study of the Fluorinated Derivatives of Singlet Phenylnitrene

2001 ◽  
Vol 123 (9) ◽  
pp. 1951-1962 ◽  
Author(s):  
Nina P. Gritsan ◽  
Anna Dóra Gudmundsdóttir ◽  
Dean Tigelaar ◽  
Zhendong Zhu ◽  
William L. Karney ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Laser Flash ◽  
Fluorinated Derivatives ◽  
Derivatives Of

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

A Laser Flash Photolysis and Pulse Radiolysis Study of Primary Photochemical Processes of Flumequine¶

2000 ◽  
Vol 72 (4) ◽  
pp. 451 ◽  
Author(s):  
M. Bazin ◽  
F. Bosca ◽  
M. L. Marin ◽  
M. A. Miranda ◽  
L. K. Patterson ◽  
...  
Keyword(s):  
Pulse Radiolysis ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Photochemical Processes
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