title: Thermolyses of O-phenyl oxime ethers. A new source of iminyl radicals and a new source of aryloxyl radicals.
abstract: Six O-phenyl ketoxime ethers, RR'C=NOPh 1-6, with RR' = diaryl, dialkyl, and arylalkyl, together with N-phenoxybenzimidic acid phenyl ether, PhO(Ph)C=NOPh, 7, have been shown to thermolyze at moderate temperatures with "clean" N-O bond homolyses to yield iminyl and phenoxyl radicals, RR'C=N(*) and PhO(*). Since 1-6 can be synthesized at room temperature, these compounds provide a new and potentially useful source of iminyls for syntheses. The iminyl from 7 undergoes a competition between beta-scission, to PhCN and PhO(*), and cyclization to an oxazole. Rate constants, 10(6) k/s(-1), at 90 degrees C for 1-6 range from 4.2 (RR' = 9-fluorenyl) to 180 (RR' = 9-bicyclononanyl), and that for 7 is 0.61. The estimated activation enthalpies for N-O bond scission are in satisfactory agreement with the results of DFT calculations of N-O bond dissociation enthalpies, BDEs, and represent the first thermochemical data for any reaction yielding iminyl radicals. The small range in k (N-O homolyses) is consistent with the known sigma structure of these radicals, and the variations in k and N-O BDEs with changes in RR' are rationalized in terms of iminyl radical stabilization by hyperconjugation: RR'C=N(*) <--> R(*)R'C[triple bond]N. Calculated N-H BDEs in the corresponding RR'C=NH are also presented.
authors.affiliation: National Research Council, Ottawa, Ontario K1A 0R6, Canada.
authors.forename: Jessie A
authors.initials: JA
authors.lastname: Blake
authors.forename: Derek A
authors.initials: DA
authors.lastname: Pratt
authors.forename: Shuqiong
authors.initials: S
authors.lastname: Lin
authors.forename: John C
authors.initials: JC
authors.lastname: Walton
authors.forename: Peter
authors.initials: P
authors.lastname: Mulder
authors.forename: K U
authors.initials: KU
authors.lastname: Ingold