A THEORETICAL STUDY OF THE 1,2,3-TRIAZOLO-IMINODIAZOMETHANE ISOMERISM IN THE GAS PHASE~#

摘要

The ring opening reactions of the 1,2,3-triazolate anion,of the three tautomers of NH-1,2,3-triazole,and of different 1,2,3-triazolium cations,to give the corresponding iminodiazomethanes,have been studied by means of ab initio calculations at the HF/6-31G~(**) level. The 1,5-electrocyclization reactions of 1,2,3-triazolate and 1H-1,2,3-triazole proceed through planar transition states with high and medium energy barriers,respectively.In both cases the cyclic forms are thermodynamically more stable than than the open-ring ones.In contrast,the decomposition of the 1,2-H-1,2,3-triazolium cation into protonated iminodiazo-methane is an exothermic process.In the last case,the preferable way of the reaction proceeds via no-aromatic intermediates (1,4H_(2-) and 1,1H_(2-)1,2,3-triazolium ions) which have a very low activation energy towards the ring opening.It has been found that there is a high #pi##pi#-conjugation between diazomethyl and imine fragments in the chain forms.