| Research Abstract |
(1) Gas phase basicities of substituted anilines toward trimethylsilyl cation have been determined by measuring trimethylsilyl cation transfer equilibria using a FT-ICR-The substituent effect on trimethylsilyl cation basicity of aniline is found to be similar to the corresponding substituent effect on proton basicity, suggesting that the Si-N bond has high covalent character. This result is consistent with that observed for acetophenone series. On the other hand, the substituent effect for Me_3Si^+basicities of stirenes was characterized by a small rho value with reduced resonance demand, suggesting that the structure of Me_3Si^+ adduct ion of stirenes with is not a open structure but a non-classical bridged one.
Relative electron affinities have been determined for a series of benzene derivatives (benzaldehydes, acetophenones, methyl benzoates, and some nitrobenzenes) by measurement of electron-transfer equilibrium in the gas phase. Substituent effects on electron affinities of these systems have successfully been described in terms of the LArSR equation. It has been shown that resonance demand parameter (r) varies significantly with the system from 0.62 for nitrobenzene, via 1.11 for benzaldehyde, to 1.29 for methyl benzoate series. The stability of a parent radical anion (ring-substituent=H) decreases in the opposite order. This trend of resonance demand is consistent with that for acidities of phenols, nilines, and toluenes, suggesting that the added electron in the SOMO of radical anions is delocalized into the aromatic ring in the same manner as that of pi-electron in the HOMO of an even-electron anion system.
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