Facultad de Medicina

Hybrid ab initio calculations (GIAO/B3LYP/6-31G*) together with new DNMR experiments (1H and 13C) have been used to clarify the problem of the conformation of 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene. The carbon-13 chemical shifts have been assigned unambiguously to the chair C and twist-boat TB conformations. Lineshape analysis of the 1H NMR spectra has been carried out at several temperatures using an estimated set of Karplus-type vicinal coupling constants.

The IH and I3C NMR spectra of the title compounds have been recorded. While the spectrum of 6,7,14,15-tetrahydrobisbenzimidazo[ 1,2-a: l',2'-e] [ i ,5]diazoeine 3 does not show any dependence with the temperature in the studied range (-65 to +75 "C), that of 6,7,13,14-tetrahydrobispyrido[1,2- a: l',2'-e] diazocinediium dibromide 4 shows a clear variation, narrow lines appearing only at + 85 "C. The differences in the dynamic behaviour of these compounds has been analyzed using different semi-empirical calculations (MNIX), AMI, PM3) of the ground and transition states. For comparison purposes, two other compounds belonging to the 6,8,6 series of ring derivatives have also been calculated, 5,6,11,12- tetrahydrodibenzo[a,e]cyclooetene 1 and 5,6,12.13 -tetrahydrobispyrazolo [ 1,2 -a: 1 ',2'-e] [ 1,2,5,6] tetrazoeinediium cation 2.

The carbon-13 chemical shifts and tH-13C coupling constants of twelve polypodal ligands belonging to bis(pyrazol-1-yl)- and tris(pyrazol-1-yl)-methane classes are described. The chemical shifts show high internal consistency: for instance, a previously-reported additive model predicts, with great accuracy, the chemical shift of the central sp3 carbon. Coupling constants proved to be useful tools for the assignment of pyrazole carbons. The 11( 1 H-13C) coupling of the central carbon is linearly related to the basicity of the pyrazole substitutent in tris(pyrazol-1-yl)methanes.

Significant information on the structure of various bisaz.olium salts of the type CA2 (C++ 2A") were revealed by the study of the FAB spectra of their positive and negative ions. Thus only one spectrum, whatever it consists of the positive or of the negative ions spectrum, enables the identification of the cation c++ and of the anion A-. Moreover, the same information are collected from the CAD spectrum of the adduct ion CA+ allowing the identification of such a compound in a mixture.

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 1 H 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 1 H NMR spectroscopy thus allowing determination of the barrier to rotation of a (dmpz) substituent (ÄG‡ = 21–22 kcal mol21 ).