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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 15 (2010) pp 113-114

Proposal for a Simple Experiment to Evaluate the Hammett Equation and the Substituent Effect on the Acidity of Benzoic Acid

Fernando H. Cincotto, Homero M. Gomes and Marcos F. S. Teixeira*

Dep. of Physical, Chemistry and Biology, Faculty of Science and Technology, University of State of Sao Paulo (UNESP); Rua Roberto Simonsen, 305–Presidente Prudente–SP, CEP 19060-900, Brazil,
Received June 6, 2008. Accepted July 10, 2009.

Published: 27 January 2010

Abstract. This work describes a simple demonstration of the Hammett constant for p-substituted benzoic acid derivatives from pH solution measurements. The procedure is based on the difference in the pH of benzoic acid and p-substituted benzoic acid solutions. The pHH – pHX values as a function of the Hammett constant (sX) show a good correlation. The experiment helps undergraduate students understand the Hammett equation and the electronic effects of substituent groups on the ionization of benzoic acids.

Key Words: Laboratories and Demonstrations; organic chemistry

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