Aromatic propellenes. Part 1. NMR spectroscopy, X-ray crystal and molecular structure of hexa(3,5-dimethylpyrazol-1-yl)benzene

The molecular and crystal structure of hexa(3,5-dimethylpyrazol-1-yl)benzene has been determined by X-ray analysis. Semiempirical calculations at the AM1 level exploring all possible symmetrical conformations of the 3,5-dimethylpyrazole rings reveal that the most stable conformation corresponds to that of the solid state in which the nitrogen atoms bearing the lone pair are placed up (u) and down (d) with respect to the benzene ring. In solution, NMR spectroscopy proves that together with conformation 1(ududud), the second most stable conformer 2(uduuud) is also present.