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Closed Access item Aromatic propellenes .8. Semiempirical calculations and DNMR studies of hexakis(pyrazol-1-yl)benzenes

Authors:Foces Foces, Concepción
Llamas Saiz,  Antonio L.
Fernández Castaño, Cristina
Claramunt, Rosa María
Escolástico,  Consuelo
Lavandera, José Luis
Santa María, María Dolores
Jimeno, M. Luisa
Elguero, José
Issue Date:1997
Publisher:Royal Society of Chemistry (Great Britain)
Citation:Journal of the Chemical Society-Perkin Transactions 2 : 2173-2177 (1997)
Abstract:The stability of all possible conformers of hexa(pyrazol-1-yl)benzene [(pz)6bz], hexakis(3,5-dimethylpyrazol-1-yl)benzene [(dmpz)6bz], 1,2,4,5-tetra(pyrazol-1-yl)-3,6-bis(3,5-dimethylpyrazol-1-yl)benzene [(pz)4(dmpz)2bz] and 1,4-di(pyrazol-1-yl)-2,3,5,6-tetrakis(3,5-dimethylpyrazol-1-yl)benzene [(pz)2(dmpz)4bz] has been determined by semiempirical AM1 calculations. In all series the absolute minimum corresponds to the conformation where the nitrogen lone pair of consecutive pyrazole rings is alternatively oriented to opposite sides of the benzene plane. The case of (pz)2(dmpz)4bz has been studied by 1H NMR studies in solution. Three isomers have been identified and all the signals assigned. The slow evolution to other isomers from those found in the solid state has been followed by 1H NMR spectroscopy thus allowing determination of the barrier to rotation of a (dmpz) substituent (ΔG‡ = 21–22 kcal mol–1)
Publisher version (URL):http://dx.doi.org/10.1039/A704257D
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