39736-41-9Relevant academic research and scientific papers
Reaction of Pyrazole Adddition to Quinones
Ballesteros, Paloma,Claramunt, Rosa M.,Escolastico, Consuelo,Maria, M. Dolores Santa,Elguero, Jose
, p. 1873 - 1876 (2007/10/02)
The reactions of pyrazole, 4-nitropyrazole, 3,5-dimethylpyrazole, and 4-chloro-3,5-dimethylpyrazole with 1,4-benzoquinone in dioxane have been analyzed.Mono- and 2,3-bis-adducts were obtained and only in the case of pyrazole was a 2,5-bis(pyrazol-1-yl)-1,
Photoinduced intramolecular proton transfer as the mechanism of ultraviolet stabilizers: A reappraisal
Catalán, Javier,Fabero, Fernando,Soledad Guijarro,Claramunt, Rosa M.,Dolores Santa María,De la Concepción Foces-Foces,Cano, Felix Hernández,Elguero, José,Sastre, Roberto
, p. 747 - 759 (2007/10/02)
Evidence based on theoretical calculations and photophysical experiments is presented to show that, contrary to general belief, the photostability of 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (Tinuvin P) cannot be explained as being due to an excited-state intramolecular proton transfer (ESIPT) through the intramolecular hydrogen bond (IMHB). Support for this conclusion comes from a related study on several members of a new family of photostable compounds, namely the 1-(2′-hydroxyphenyl)pyrazoles, which were obtained by the reaction of pyrazole and of 3,5-dimethylpyrazole with benzoquinone. The structures of these pyrazole derivatives, namely 2,3-bis(3′,5′-dimethylpyrazol-1′-y1)-, 2,3-bis(pyrazol-1′-y1)-, 2-(pyrazol-1′-y1)-, and 2,5-bis(pyrazol-1′-y1)-1,4-dihydroxybenzene (1, 2, 3, and 4, respectively) were established by spectroscopic techniques and X-ray crystallography. Both derivatives 3 and 4 possess a strong intramolecular hydrogen bond and are reasonably photostable; derivatives 1 and 2 appear, however, to possess only a weak intramolecular hydrogen bond. 1 and 3 pack in helical systems, 4 does it with intercrossing stacking, and 2-H2O has a three-dimensional network involving water molecules.
