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.