Annular elementotropy

A-Dialkylaminomethylbenzotriazoles usually exist in the crystalline state solely as the N(l) isomers, but in solution they form equilibrium mixtures of the N(l) (209, 210) and N(2) (211) isomers 75JCS(Pl)l 181, 87JCS(Pi)2673). The N(l) and N(2) isomers are of nearly equal stability in nonpolar solvents and in the gas phase (2 1 ratio on statistical grounds). Polar solvents favor the 1- and 3-substituted forms over the 2-substituted, and conversely substituents at positions four and seven favor the 2-substituted form. The interconversion of these N(l) and N(2) isomers proceeds intermolecularly, as demonstrated by cross-over experiments, by a dissociation-recombination mechanism involving the formation of intermediate iminium cations and the benzotriazole anion. 

Under flash vacuum pyrolysis conditions 1- and 2-(l-adamantyl)indazoles as well as 1-, 2- and 3-tritylindazoles are mutually interconverted (91BSF592, 89BSB349). 

Enthalpies of gas-phase thermal isomerisations of 1-methyl- to 2-methyltetrazoles have been reported to be small (2.1-3.9 kJ mol ) (90ZPH656). 

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Annular elementotropy - This is a type of tautomerism involving the reversible migrations of organic and inorganic groups that are analogous to those of a proton in annular tautomerism. For examples see Section 2.4.5.1.2. 

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