FACTORS AFFECTING RATES OF THERMAL-DECOMPOSITION OF 5-AZIDOPYRAZOLES - A COMPARISON WITH OTHER AROMATIC AZIDES

2-Methoxyazidobenzene has been used as a model compound for alpha-azid o five-membered heterocycles, and undergoes thermal loss of nitrogen 1 6 times as fast as azidobenzene and 3.6 times as fast as its para isom er. These rates identify an important electrostatic stabilization with in a charge-separated transition state. It is argued that this stabili zation would be very much larger in thermolyses of alpha-azido five-me mbered heterocycles and removes the need to postulate that their high rates are due to appreciable ring-opening at the transition state. Ele ctronic effects of ring substituents in 5-azidopyrazoles are consisten t with this electrostatic model. The electron distribution required is not compatible with the operation of a neighbouring group effect, and none is found for 5-azido-4-nitro-pyrazole.