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Título : Aromatic propellenes .8. Semiempirical calculations and DNMR studies of hexakis(pyrazol-1-yl)benzenes
Autor : 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
Fecha de publicación : 1997
Editor: Royal Society of Chemistry (Great Britain)
Citación : Journal of the Chemical Society-Perkin Transactions 2 : 2173-2177 (1997)
Resumen: 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)
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ISSN: 0300-9580
DOI: 10.1039/A704257D
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