The C₆H₅N energy surface. IV. Isotopic labelling studies in phenylnitrene isomerizations

Abstract

Gas phase pyrolysis of phenyl azide gives rise to aniline, cyclopentadienecarbonitrile and pyridine as isomerization products from phenylnitrene. Isotopic labelling studies (¹⁴C, ¹³C) are used to examine the isomerization processes which occur in phenylnitrene prior to product formation.     At the lowest energy level of the intermediate little or no label randomization occurs and aniline evidently arises from hydrogen capture at this stage. Higher levels of the intermediate involve a cycloperambulatory motion of the nitrene nitrogen atom, followed by ring contraction to cyclo- pentadiene-1-carbonitrile. The pyridine formed possibly arises from a ring-expanded intermediate, which may not have undergone the cycloperambulation of the nitrene nitrogen atom.   The aniline and cyanocyclopentadiene derived from 5- pyridyltetrazole pyrolysis appear to exhibit very similar behaviour to those from phenyl azide as far as isotopic migration is concerned.