T. Kuivalainen et al., FRAGMENTATION OF PROTONATED O,O-DIETHYL O-ARYL PHOSPHOROTHIONATES IN TANDEM MASS-SPECTRAL ANALYSIS, Journal of the American Society for Mass Spectrometry, 7(2), 1996, pp. 189-197
The gas-phase ion chemistry of protonated O,O-diethyl O-aryl phosphoro
thionates was studied with tandem mass spectrometric and ab initio the
oretical methods. Collision-activated dissociation (CAD) experiments w
ere performed for the [M + H](+) ions on a triple quadrupole mass spec
trometer. Various amounts of internal energy were deposited into the i
ons upon CAD by variation of the collision energy and collision gas pr
essure. In addition to isobutane, deuterated isobutane C4D10 also was
used as reagent gas in chemical ionization. The daughter ions [M (+) H
- C2H4](+) and [M + H - 2C(2)H(4)](+) dominate the CAD spectra. These
fragments arise via various pathways, each of which involves gamma-pr
oton migration. Formation of the terminal ions [M + H - 2C(2)H(4) - H2
O](+), [M + H - 2C(2)H(4) - H2S](+), [ZPhOH(2)](+), [ZPhSH(2)](+), and
[ZPhS](+) [Z = substituent(s) on the benzene ring] suggests that (1)
the fragmenting [M + H](+) ions of O,O-diethyl O-aryl phosphorothionat
es have protons attached on the oxygen of an ethoxy group and on the o
xygen of the phenoxy group; (2) thiono-thiolo rearrangement by aryl mi
gration to sulfur occurs; (3) the fragmenting rearranged [M + H](+) io
ns have protons attached on the oxygen of an ethoxy group and on the s
ulfur of the thiophenoxy group. To get additional support for our inte
rpretation of the mass spectrometric results, some characteristics of
three protomers of O,O-diethyl O-phenyl phosphorothionate were investi
gated by carrying out ab initio molecular orbital calculations at the
RHF/3-21G level of theory.