An NMR experimental and theoretical study of pyrazagalloles, the gallium analogues of pyrazaboles.

Five pyrazagalloles bearing H and CH3 substituents on the gallium atom and/or in the pyrazole ring have been calculated. The theoretical results have been compared with literature results concerning geometries from the Cambridge Data Base with very good agreement. 1H and 13C NMR results from the literature, scarce, and unpublished from our group are also well reproduced from GIAO calculations. The most important conclusion from this work is the assignment to a pz3Ga3 trimer as the isomer present in the 1H NMR spectra of dimeric pyrazagalloles. A mechanism connecting dimers and trimers has been found and the transition states identified. [ABSTRACT FROM AUTHOR]