Aromatic propellenes. Part 3. NMR, X-ray crystallography and semi-empirical calculations on the conformational isomerism of 1,2,4,5-tetrakis (pyrazol-1′-yl)-3,6-bis(3″,5″-dimethylpyrazol-1′-yl) benzene
✍ Scribed by Concepcion Foces-Foces; Cristina Fernández-Castaño; Rosa María Claramunt; Consuelo Escolástico; José Elguero
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 494 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0894-3230
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✦ Synopsis
The molecular and crystal structures of two crystalline forms of 1,2,4,5-tetrakis(pyrazol-l'-yl)-3,6-bis(3",5"dimethylpyrazol-1"-yl) benzene and one inclusion complex with two molecules of acetic acid were determined by x-ray analysis. The acetic acid forms dimers through symmetry centers and the only interactions in the structures are mainly due to weak C-H...N interactions. All 14 possible conformations of the pyrazole with regard to the benzene ring were explored by means of AM1 semi-empirical calculations. The observed conformation in the crystal structures agrees fairly well with the most stable conformation which presents the pyrazole rings with the N(2) alternating between both sides of the phenyl plane. These calculations allow one to identify the minor isomer present in solution together with the major isomer corresponding to the crystal structure.