Stability and reactivity of the benzyl and tropylium cations in the gas phase

<jats:p> A measurement of equilibrium [4]: t-C<jats:sub>4</jats:sub>H<jats:sub>9</jats:sub><jats:sup>+</jats:sup> + BzCl = t-C<jats:sub>4</jats:sub>H<jats:sub>9</jats:sub>Cl + C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> led to equilibrium constants K<jats:sub>4</jats:sub> which are in fair agreement with earlier work by Abboud etal. However, the present temperature dependence predicts a ΔS<jats:sub>4</jats:sub><jats:sup>0</jats:sup> which is sufficiently different from that by Abboud etal. to put in question the indentification of C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> as Bz<jats:sup>+</jats:sup> on the basis of the measured ΔS<jats:sub>4</jats:sub><jats:sup>0</jats:sup> value. Therefore experiments were made to confirm that C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> produced in [4] is Bz<jats:sup>+</jats:sup> and not the tropylium cation. A C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> cation was produced by hydride abstraction from 1,3,5-cycloheptatriene. The behaviour of that C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> ion was entirely different from C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> produced by chloride abstraction from BzCl or hydride abstraction from toluene. While the benzyl derived C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> engaged in a number of reactions like hydride abstraction, chloride abstraction, addition, condensation, etc., the C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> from the heptatriene remained completely unreactive. On this basis the C<jats:sub>7</jats:sub>H<jats:sub>7</jats:sub><jats:sup>+</jats:sup> ions were identified as Bz<jats:sup>+</jats:sup> and tropylium<jats:sup>+</jats:sup>, respectively. Rate constants for several reactions of Bz<jats:sup>+</jats:sup> were determined. It is concluded that a rearrangement from benzyl to tropylium cations and vice versa does not occur at least up to 300 °C. The ions also retain their identity if they are produced with considerable internal excitation energy. </jats:p>