Ion-Molekül-Reaktionen und Hammett-Gleichung

✍ Scribed by H.-D. Klotz; H. Drost

• Publisher: John Wiley and Sons
• Year: 1972
• Tongue: English
• Weight: 445 KB
• Volume: 6
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210060604

✦ Synopsis

In order to determine the relationship between elementary ion-molecule reactions in the gas phase and certain steps of chemical reactions in the liquid phase, we have tried to model the formation of u-complexes as part of the electrophilic aromatic substitution reaction by means of a proton transfer reaction to aromatic molecules. The Hammett equation should provide the necessary criteria for such a relationship.

The comparison of the Hammett a-constants with the cross section ratios for the proton transfer reaction of unsubstituted and substituted aromatics-the latter being representative of the corresponding reaction rate constants-does not yield a linear relationship and therefore suggests that the Hammett equation is not valid in the domain of gas phase reactions. If, on the other hand, the a-constants are set in relation with the proton affinity PA, i.e. with the energy released during the formation of a a-complex, a linear or otherwise well-defined relationship results. This observation was taken to be an indication of the fact that the Hammett equation is also valid in the case of ion-molecule reactions.