Silicon- versus carbon-containing ions: 1,3-CH3+ transfers

Abstract : In the second field-free region of a double focusing mass spectrometer, the spontaneous fragmentation of the (CH3)(3)C-O-C+ (CD3)(2) ion is not preceded by direct methyl cation migrations. In contrast, a complete exchange of the methyl groups occurs prior to dissociation of the (CH3)(3)Si-O-Si+(CD3)(2) ion. This is in agreement with the calculated energy diagram which shows that two factors explain this behavior. (i) The simple cleavage of (CH3)(3)C-O-C+(CD3)(2) giving (CH3)(3)(C+) only requires 25.8 kcal mol(-1) while the corresponding fragmentation in (CH3)(3)Si-O-Si+(CD3)(2) necessitates 74.2 kcal mol(-1). (ii) The transition state for the 1,3-CH3+ transfer from carbon to carbon lies in energy 59.1 kcal mol(-1) above the covalent structure (CH3)(3)C-O-C+(CD3)(2) and only 12.4 kcal mol(-1) for the 1,3-CH3+ transfer from silicon to silicon. Calculations and experiments show that the situation is intermediate for the 1,3-CH3+ from silicon to carbon. (Cop) 2002 Published by Elsevier Science B.V.
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Hristo Nedev, J.-P. Denhez, D. Leblanc, Henri Audier. Silicon- versus carbon-containing ions: 1,3-CH3+ transfers. International Journal of Mass Spectrometry, Elsevier, 2002, 217 (1-3), pp.245-255. ⟨10.1016/S1387-3806(02)00575-4⟩. ⟨hal-00918100⟩

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