THE PHOTOCHEMISTRY OF VARIOUS PARASUBSTITUTED TETRAFLUOROPHENYL AZIDES IN ACIDIC MEDIA AND THE FORMATION OF NITRENIUM IONS

Laser flash photolysis of polyfluorinated aryl azides in acetonitrile at ambient temperature produces singlet nitrenes which have lifetimes of tens to hundreds of nanoseconds. The lifetimes are controlled by ri ng expansion and intersystem crossing to the lower energy triplet stat e. In the presence of sulfuric acid the singlet nitrene can be protona ted to form a new species whose transient absorption is attributed to a nitrenium ion. This assignment is based in part on analogy to other itrenium ion spectra and studies reported recently by Falvey (J. Am. C hem. Sec. 1993, 115, 7254) and McClelland and Novak (J. Am. Chem. Sec. 1994, 116, 4513) and to the protonation ofp-biphenylnitrene reported by Davidse et al. (J. Am. Chem. Sec. 1993, 116, 4513). The polyfluorin ated nitrenium ions likely have singlet ground states, consistent with recent calculations of the parent structure.