Abstract
G2(+) level molecular orbital calculations have been carried out for the identity nucleophilic substitution at saturated oxygen, X- + HOX → HOX + X- (X = F, Cl, Br, I). A comparison with data for the analogous reactions at saturated nitrogen, X- + NH2X → NH2X + X-, and at saturated carbon, X- + CH3X → CH3X + X-, indicate that the substitution reaction at saturated oxygen proceeds via a classic SN2 pathway. The calculated intrinsic barriers ΔHcent≠ for substitution at oxygen are found to be much higher than the corresponding barriers for substitution at carbon and nitrogen, decreasing in the order F(106.3 kJ/mol) > Cl(92.5 kJ/mol) > Br(70.3 kJ/mol) > I(58.6 kJ/mol). Stabilization energies of the ion-molecule complexes decrease in the order F(187.9 kJ/mol) > Cl(97.5 kJ/mol) > Br(81.2 kJ/mol) > I(66.5 kJ/mol), that are also significantly higher than the corresponding values at carbon and nitrogen, and correlate well with the halogen electronegativities. The overall barriers relative to the reactants (ΔHovr≠) are negative for all halogens F(-81.7 kJ/mol), Cl(-5.1 kJ/mol), Br(-10.7 kJ/mol), I(-8.1 kJ/mol). These trend is similar to that for the analogous reaction at nitrogen, but contrasts to that for the reactions at carbon where the ΔHovr≠ are negative only for X = F.
Original language | English |
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Pages (from-to) | 1-10 |
Number of pages | 10 |
Journal | International Journal of Mass Spectrometry |
Volume | 220 |
Issue number | 1 |
DOIs | |
State | Published - 15 Sep 2002 |
Bibliographical note
Funding Information:This work was supported by the Barbara and Kort Sino-Israel Post-Doctoral Fellowship Program.
Funding
This work was supported by the Barbara and Kort Sino-Israel Post-Doctoral Fellowship Program.
Funders | Funder number |
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Barbara and Kort Sino-Israel |
Keywords
- Ab initio calculation
- Reaction mechanism
- S2 at neutral oxygen