Spectroscopic characterization by laser flash photolysis of electrophilic intermediates derived from 4-aminostilbenes. Stilbene “nitrenium” ions and quinone methide imines †

1999 ◽  
pp. 1591-1600 ◽  
Author(s):  
Rohit Bose ◽  
Abid R. Ahmad ◽  
Andrew P. Dicks ◽  
Michael Novak ◽  
Kelly J. Kayser ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Spectroscopic Characterization ◽  
Laser Flash ◽  
Quinone Methide ◽  
Nitrenium Ions

Structures of Reactive Nitrenium Ions:  Time-Resolved Infrared Laser Flash Photolysis and Computational Studies of SubstitutedN-Methyl-N-arylnitrenium Ions

2000 ◽  
Vol 122 (34) ◽  
pp. 8271-8278 ◽  
Author(s):  
Sanjay Srivastava ◽  
Patrick H. Ruane ◽  
John P. Toscano ◽  
Michael B. Sullivan ◽  
Christopher J. Cramer ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Infrared Laser ◽  
Computational Studies ◽  
Time Resolved ◽  
Nitrenium Ions ◽  
Arylnitrenium Ions

1995 Merck Frosst Award Lecture Quinone methides: relevant intermediates in organic chemistry

1996 ◽  
Vol 74 (4) ◽  
pp. 465-475 ◽  
Author(s):  
Peter Wan ◽  
Beverly Barker ◽  
Li Diao ◽  
Maike Fischer ◽  
Yijian Shi ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Aqueous Media ◽  
Laser Flash ◽  
Alder Reaction ◽  
Quinone Methide ◽  
Quinone Methides ◽  
Chemical Systems ◽  
The One ◽  
Chroman Ring

ortho and para-Quinone methides (2-methylene-3,5-cyclohexadien-1-one and 4-methylene-2,5-cyclohexadien-1-one, respectively) are intermediates in a variety of important chemical systems. In particular, o-quinone methides are useful in synthesis for the construction of chroman ring systems. A brief account of the relevance of quinone methide chemistry will be provided. This is followed by a review of recent studies from our laboratory on efficient methods for the photogeneration of quinone methides, concentrating on the use of hydroxy-substituted benzyl alcohols in aqueous media. It is shown that this method is general since it provides access to o-, m-, and p-quinone methide isomers. When appropriately substituted, all of these quinone methide isomers have been spectroscopically characterized by laser flash photolysis, making this technique the one of choice for studying the dynamics of these reactive intermediates. The mechanism of photochemical generation from hydroxybenzyl alcohols and extensions of the reaction to photogeneration of fluorenyl and biphenyl quinone methides will also be presented. Key words: quinone methide, biphenyl quinone methide, carbocation, photosolvolysis, photodehydroxylation, hetero-Diels–Alder reaction.

Mechanistic studies of photohydration of m-hydroxy-1,1-diaryl alkenes

2002 ◽  
Vol 80 (1) ◽  
pp. 46-54 ◽  
Author(s):  
John G Cole ◽  
Peter Wan
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Parent Compound ◽  
Laser Flash ◽  
Intramolecular Proton Transfer ◽  
Quinone Methide ◽  
Quantum Yields ◽  
Nanosecond Laser

The photohydration of a variety of m-hydroxy-1,1-diaryl alkenes (8–10) and related systems (11 and 12) has been studied in aqueous CH3CN solution. All of these alkenes photohydrate efficiently in 1:1 H2O–CH3CN, to give the corresponding 1,1-diarylethanol (Markovnikov addition) products with high chemical and quantum yields. The aim of this study was to further probe the mechanism of photohydration reported for the parent m-hydroxy-α-phenylstyrene (5), which has been proposed as consisting of a water trimer-mediated excited state (formal) intramolecular proton transfer (ESIPT) from the phenolic proton to the β-carbon of the alkene moiety to give an observable (by laser flash photolysis (LFP)) m-quinone methide intermediate 6. For this purpose, derivatives of 5 with substituents (methyl or methoxy) on the α-phenyl ring as well as related model compounds were explored. Product studies, quantum yields, fluorescence, and nanosecond laser flash data are reported that are consistent with two distinct mechanisms for photohydration of these compounds: one involving water-mediated ESIPT (8, 9), as observed for the parent compound 5, and one involving direct protonation of the β-carbon by solvent water (11 and 12), with compound 10 possibly operating via both mechanisms.Key words: photohydration, solvent-assisted excited state intramolecular proton transfer (ESIPT), m-quinone methide, diarylmethyl carbocation.

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

Laser Flash Photolysis Studies of the UVA Sunscreen Mexoryl® SX

1999 ◽  
Vol 70 (3) ◽  
pp. 292
Author(s):  
Ann Cantrell ◽  
David J. McGarvey ◽  
Louise Mulroy ◽  
T. George Truscott
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash
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