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Fragmentations and reactions of protonated O,O-dimethyl ethylphosphonate and some isotoporners produced by electrospray ionisation in an ion trap mass spectrometer

Fragmentations and reactions of protonated O,O-dimethyl ethylphosphonate and some isotoporners produced by electrospray ionisation in an ion trap mass spectrometer
Fragmentations and reactions of protonated O,O-dimethyl ethylphosphonate and some isotoporners produced by electrospray ionisation in an ion trap mass spectrometer
The fragmentation behaviour of protonated O,O-dimethyl ethylphosphonate and its isotopomers deuterated in the ?- and ?-positions of the ethyl group and their fragment ions, particulary EtP(O)OMe+(IV), have been investigated both experimentally in an ion trap mass spectrometer and theoretically by electronic structure calculations at the B3LYP level. Of particular interest is the finding that the phosphonium ion IV eliminates ethene with hydrogen/deuterium loss from both the ?-and ?-positions. The initial step for both routes involves ethyl migration from P to O to form the ion MeOP+OEt which then loses ethene by two mechanisms, both of which lead to the same products. That a unitary branching ratio for ?- and ?-elimination is not observed indicates that although the final step of dissociation into product ion and ethene is energetically the most demanding, it is not rate limiting and the large entropy change associated with the dissociation allows earlier processes to determine the branching ratio. This demonstrates once again that free energy, not enthalpy (or energy), determines the course of gas phase ion processes.
mass spectrometry, electrospray, ion trap, organophosphates, fragmentations
1387-3806
46-54
Bell, A.J.
a3daf8c9-3047-4f42-8038-b839ff6ec575
Ferrante, F.
cff3f6ec-876e-45c4-bb06-ac2734fdd3ee
Hall, S.E.
d57bd610-d896-4e6d-9a40-31bbaf5d84a0
Mikhailov, V.
1969e3f0-f83d-4bd7-9e2f-acccdba72bd3
Mitchell, D.
e93a76d4-9e0e-4dc1-ae77-0fdb20cf62f4
Timperley, C.M.
edc8d723-7947-45ad-9de8-65474e0f4d15
Watts, P.
98213bc9-aedd-4341-aab0-cfb019b73aeb
Williams, N.
54385e30-6b7c-4eec-b904-bd3f9c9dedbb
Bell, A.J.
a3daf8c9-3047-4f42-8038-b839ff6ec575
Ferrante, F.
cff3f6ec-876e-45c4-bb06-ac2734fdd3ee
Hall, S.E.
d57bd610-d896-4e6d-9a40-31bbaf5d84a0
Mikhailov, V.
1969e3f0-f83d-4bd7-9e2f-acccdba72bd3
Mitchell, D.
e93a76d4-9e0e-4dc1-ae77-0fdb20cf62f4
Timperley, C.M.
edc8d723-7947-45ad-9de8-65474e0f4d15
Watts, P.
98213bc9-aedd-4341-aab0-cfb019b73aeb
Williams, N.
54385e30-6b7c-4eec-b904-bd3f9c9dedbb

Bell, A.J., Ferrante, F., Hall, S.E., Mikhailov, V., Mitchell, D., Timperley, C.M., Watts, P. and Williams, N. (2008) Fragmentations and reactions of protonated O,O-dimethyl ethylphosphonate and some isotoporners produced by electrospray ionisation in an ion trap mass spectrometer. International Journal of Mass Spectrometry, 269 (1-2), 46-54. (doi:10.1016/j.ijms.2007.09.004).

Record type: Article

Abstract

The fragmentation behaviour of protonated O,O-dimethyl ethylphosphonate and its isotopomers deuterated in the ?- and ?-positions of the ethyl group and their fragment ions, particulary EtP(O)OMe+(IV), have been investigated both experimentally in an ion trap mass spectrometer and theoretically by electronic structure calculations at the B3LYP level. Of particular interest is the finding that the phosphonium ion IV eliminates ethene with hydrogen/deuterium loss from both the ?-and ?-positions. The initial step for both routes involves ethyl migration from P to O to form the ion MeOP+OEt which then loses ethene by two mechanisms, both of which lead to the same products. That a unitary branching ratio for ?- and ?-elimination is not observed indicates that although the final step of dissociation into product ion and ethene is energetically the most demanding, it is not rate limiting and the large entropy change associated with the dissociation allows earlier processes to determine the branching ratio. This demonstrates once again that free energy, not enthalpy (or energy), determines the course of gas phase ion processes.

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More information

Submitted date: 22 June 2007
Published date: 2008
Keywords: mass spectrometry, electrospray, ion trap, organophosphates, fragmentations

Identifiers

Local EPrints ID: 54424
URI: https://eprints.soton.ac.uk/id/eprint/54424
ISSN: 1387-3806
PURE UUID: 88adc681-cb9f-4e2d-9642-cd3ed487c96c

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Date deposited: 06 Aug 2008
Last modified: 13 Mar 2019 20:38

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Contributors

Author: A.J. Bell
Author: F. Ferrante
Author: S.E. Hall
Author: V. Mikhailov
Author: D. Mitchell
Author: C.M. Timperley
Author: P. Watts
Author: N. Williams

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