ISSN:
0894-3230
Keywords:
Chemistry
;
Theoretical, Physical and Computational Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The molecular and crystal structures of two crystalline forms of hexa(pyrazol-1-yl)benzene were determined by x-ray analysis. They correspond to two conformational polymorphs: form I is obtained in acetic acid and form II in ethanol or dichloromethane. The crystal packing of both conformers is different; however, that of form I is analogous to that of hexa(3,5-dimethylpyrazol-1-yl)benzene, having similar cell dimensions and space groups R-3. No significant interactions except the van der Waals interactions were observed. Semiempirical calculations at the AM1 and SAM1 levels, exploring all possible conformations of the pyrazole rings, reveal that the most stable conformation presents the pyrazole rings with the N(2) alternating between both sides of the phenyl plane as it occurs in the solid state, crystalline form I (conformation 8h). The computed minimum energy for conformer 7a, which is related to crystal form II, presents a different sequence of pyrazole arrangements [N(2) up or down] and is only 1·6-2·0 kcal mol-1 less stable than the previous one in both parametrizations. The SAM1 method yields pyrazole moieties more perpendicular to the benzene ring than the AM1 one.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
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