Dv. Ramana et E. Kantharaj, INTRAMOLECULAR AROMATIC-SUBSTITUTION AND ORTHO INTERACTIONS IN SUBSTITUTED 1-PHENYL ETHANONE AND DIPHENYLMETHANONE OXIMES ON ELECTRON-IMPACT, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 36(9), 1997, pp. 776-781
The formation of the ions at m/z 133 and 195 from the molecular ions o
f substituted 1-(phenyl)ethanone oximes and diphenylmethanone oximes h
as been identified to be due to the expulsion of RH, wherein R is the
substituent present in the phenyl ring, for which are assigned 3-methy
lbenz-1,2-isoxazole and 3-phenylbenz-1,2-isoxazole radical cation stru
ctures respectively based on CAD spectral study. A mechanism involving
an initial intramolecular aromatic substitution of the oxygen atom of
the oxime hydroxyl group on the ortho carbon leading to the distonic
ion from which a 1,2-elimination of the ortho substituent along with t
he hydrogen of the hydroxyl group is proposed for the elimination of R
H. Substituent scrambling in the distonic ion has been invoked for the
loss of RH from certain para substituted derivatives. An important fr
agment ion at m/z 181 has been noticed in the mass spectra of (2-metho
xyphenyl)phenylmethanone oxime due to ortho interaction during the sec
ondary fragmentation process. The proposed mechanism for these process
es and the ion structures are supported by high-resolution data, B/E a
nd B-2/E linked-scan spectra and CAD/B/E spectra.