The relative electron-releasing power of a singly bound, and the electron-attracting power of a doubly bound nitrogen atom when present in the same five-membered ring

Abstract

The kinetics of reaction between various bromo-N-methyl-tetrazoles, -trizoles, or -imidazoles and piperdine in ethanol have been measured.

5-Bromo-1-methyltetrazole is appreciably more reactive than 5-bromo-1-methyl- or 5-bromo-4-methyl-1,2,4-triazole or 4-bromo-1-methyl-1,2,3-triazole, whereas 2-bromo-1-methyl- and 5-bromo-1-methyl-imidazole failed to react at 200°. Similarly 5-bromo-2-methyltetrazole is more reactive than 4-bromo-2-methyl-1,2,3-triazole.

The low reactivity of the 2-methyl derivatives, compared with these 1-methyl isomers, is attributed to less stabilisation in the transitions state. 5-Bromo-4-methyl-1,2,4-triazole is also less reactive than its 1-methyl isomer.

Comparison of these results with those obtained for 2-bromopyridine indicates that from two to three doubly bound nitrogen atoms are required in azoles to overcome electron-release from the singly bound atom and reach the reactivity of the bromopyridine; but large positional effects are also observed.

5-Bromo-1-methyl-1,2,3-triazole reacts anomalously by not obeying second-order kinetics.

An exocyclic nitro-substituent in imidazole is more activating than a doubly bound ring nitrogen in the corresponding bromotriazole.

Arrhenius parameters are discussed. Ionisation constants and ultraviolet spectra of starting materials and products are recorded.