Loss of CO2 from the ortho isomer of deprotonated methyl phenyl carbonate involves a methyl migration
Date
2001
Authors
Mc Anoy, A.
Dua, S.
Rees, K.
Bowie, J.
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Journal article
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International Journal of Mass Spectrometry, 2001; 210(1-3 Special Issue SI):557-562
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Andrew M. McAnoy, Suresh Dua, Kylee Rees and John H. Bowie
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Abstract
The collision induced decompositions of the ortho-, meta, and para- (M-H)<sup>-</sup> anions of methyl phenyl carbonate were studied to see whether there is loss of CO<inf>2</inf> occurring by the benzyne cine-substitution {(C<inf>6</inf>H<inf>4</inf>)<sup>-</sup>-OCO<inf>2</inf>Me→ [(C<inf>6</inf>H<inf>4</inf>)MeOCO<inf>2</inf><sup>-</sup>]→ (C<inf>6</inf>H<inf>4</inf>)<sup>-</sup>-OMe+CO<inf>2</inf>}. Loss of CO<inf>2</inf> is observed from the ortho isomer, but the process does not involve a benzyne cine substitution. It is a methyl migration through a six-centre transition state to give a cresol (M-H)<sup>-</sup> ion, probably ortho-MeC<inf>6</inf>H<inf>4</inf>-O<sup>-</sup>. Theoretical calculations [at the B3LYP/6-311++G(d,p)//HF/3-21+G(d) level of theory] indicate the methyl migration is a stepwise process, with the barrier for the first (and rate determining) step being 191 kJ mol<sup>-1</sup>. The overall process is calculated to be exothermic by 276 kJ mol<sup>-1</sup>. © 2001 Elsevier Science B.V.
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Copyright © 2001 Elsevier Science B.V. All rights reserved.