PYROLYSIS OF ARYL AZIDES .13. CONFORMATIONAL EFFECTS ON THE ABILITY OF CARBONYL AS A NEIGHBORING GROUP

Our previous claim,(1) that locking an ortho carbonyl group into a fav ourable conformation causes very large increases in the rate of thermo lysis of aryl azides, has been reexamined. In 8-azido-5-methoxy-1-tetr alone the rate advantage over an azide with a rotatable ortho acetyl g roup is estimated to be only 18-fold. Nevertheless, this factor is lar ge enough to invalidate attempts to explain relative neighbouring grou p abilities on simple electronic effects alone. The very large rate in creases we reported previously for 1-azidoacridin-9(10H)-one and 1-azi doanthracene-9,10-dione are partly due to favourable retention of conj ugation in the transition state.