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Basicité des Amines et de Nicotines : Liaison Hydrogène et Protonation.

Abstract : The most characteristic property of amines is their ability to behave as bases. We have then measured a type of basicity that has never been really studied at that time, their hydrogen bonding basicity. We have determined the thermodynamic parameters, ∆G, ∆H and ∆S, of the hydrogen bond complexation of 4-fluorophenol with about a hundred amines. We have also determined the spectroscopic scale of hydrogen bond basicity, ∆ν(OH) and showed that each of the three scales makes its contribution to the knowledge of the basicity of amines. The study of different empirical (substituent effects) and theoretical (electrostatic potential, electronic energy variation by complexation) parameters of hydrogen bonding basicity is investigated. The lipophilicity of about 100 nitrogen bases is successfully predicted with only two structural parameters : the molar volume and the Gibbs energy of hydrogen bonding. We show moreover that the hydrogen bond basicity scale is very different of the scales of Brönsted basicity pKa in aqueous solutions or GB in the gas phase. In a second part, we study the ability of nicotine and nornicotine to form hydrogen bonds and to protonate in the gas phase with the aim of analysing the potential interactions between these molecules and their receptors. Indeed, nicotine has two competitive basic sites : an amino nitrogen and a pyridine nitrogen. We show that, for nicotine and nornicotine, the amino nitrogen is a secondary hydrogen bond acceptor site which is at the origin of the lipophilicity of these bases. In gas phase, the protonation site of nornicotine is the pyridine nitrogen, favoured by an intramolecular hydrogen bond CHLN. Nevertheless, the proton basicities of the two nicotine nitrogens seem to be very similar.
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Submitted on : Monday, September 4, 2006 - 3:14:59 PM
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Jerome Graton. Basicité des Amines et de Nicotines : Liaison Hydrogène et Protonation.. Autre. Université de Nantes, 2001. Français. ⟨tel-00090950⟩

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