Charge-remote fragmentation and the two-step elimination of alkanols from fast atom bombardment-desorbed (M + H)(+), (M + Cat) (+), and (M - H) (-) ions of aromatic β-hydroxyoximes.
Aromatic β-hydroxyoximes undergo unusual fragmentation reactions as protonated or cationized species, as radical cations, or as (M - H)(-) ions, As protonated species, they expel OH ' from the oxime functionality in violation of the even electron rule. Parallel eliminations of alkyl radicals follow OH' loss when the aromatic ring is substituted with an alkyl chain. Alkyl radical losses appear to be characteristic of radical cations that can isomerize to ions in which the alkyl chain bears a radical site and the charged site is the conjugate acid of a basic functionality (e.g., oxime or imine). Evidence for the mechanisms was found in the ion chemistry of oxime and imine radical cations. The imine reference compounds were conveniently generated by fast atom bombardment-induced reduction of oximes, removing the requirement for using conventional chemical synthesis. Protonated imines and the (M - H)(-) ions of oximes fragment extensively via charge-remote processes to eliminate the elements of alkanes. This chemistry is not shared by the protonated oximes.
Department of Chemistry, University of Aveim, 3800 Aveiro, Portugal.
M G
MG
Santana-Marques
A J
AJ
Ferrer-Correia
K A
KA
Caldwell
M L
ML
Gross