The methylation of alfa,omega-diphenylalkanes (C6H5(CH2)nC6H5, n ) 1-6) has been performed in the gas phase using Me2Cl+ ions as alkylating species and toluene as reference substrate. Both in radiolytic experiments at atmospheric pressure and in FT-ICR measurements at 10-8 Torr, the selected diphenylalkanes reacted faster than toluene, the highest reactivity displayed by 1,3-diphenylpropane. The kinetic pattern of the reaction, conforming to the established scheme of an electrophilic alkylation reaction, is consistent with a rate-determining formation of the sigma-complex intermediate, at variance with the tert-butylation of the same series of compounds by Me3C+ ions, occurring at the collisional encounter rate. The kinetic features are explained by a marked effect due to the presence of the second aryl ring, providing additional stabilization of both the ion-neutral collision complex and the sigma complex with respect to toluene. Both factors contribute to the deltaEa of ca. 8 kcal mol-1 for the competition of 1,3-diphenylpropane and toluene found in the temperature dependence study of the Me2Cl+ reaction.

Cation-π Interactions in the Gas Phase Methylation of α, ω-Diphenylalkanes / Chiavarino, Barbara; Crestoni, Maria Elisa; Fornarini, Simonetta; D., Kuck. - In: JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY. - ISSN 1089-5639. - STAMPA. - 107:(2003), pp. 4619-4624.

Cation-π Interactions in the Gas Phase Methylation of α, ω-Diphenylalkanes .

CHIAVARINO, Barbara;CRESTONI, Maria Elisa;FORNARINI, Simonetta;
2003

Abstract

The methylation of alfa,omega-diphenylalkanes (C6H5(CH2)nC6H5, n ) 1-6) has been performed in the gas phase using Me2Cl+ ions as alkylating species and toluene as reference substrate. Both in radiolytic experiments at atmospheric pressure and in FT-ICR measurements at 10-8 Torr, the selected diphenylalkanes reacted faster than toluene, the highest reactivity displayed by 1,3-diphenylpropane. The kinetic pattern of the reaction, conforming to the established scheme of an electrophilic alkylation reaction, is consistent with a rate-determining formation of the sigma-complex intermediate, at variance with the tert-butylation of the same series of compounds by Me3C+ ions, occurring at the collisional encounter rate. The kinetic features are explained by a marked effect due to the presence of the second aryl ring, providing additional stabilization of both the ion-neutral collision complex and the sigma complex with respect to toluene. Both factors contribute to the deltaEa of ca. 8 kcal mol-1 for the competition of 1,3-diphenylpropane and toluene found in the temperature dependence study of the Me2Cl+ reaction.
Gas phase radiolysis; cation-pi interactions; Gas phase kinetics; reaction mechanisms
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Cation-π Interactions in the Gas Phase Methylation of α, ω-Diphenylalkanes / Chiavarino, Barbara; Crestoni, Maria Elisa; Fornarini, Simonetta; D., Kuck. - In: JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY. - ISSN 1089-5639. - STAMPA. - 107:(2003), pp. 4619-4624.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/71350
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