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The Chemical Educator
ISSN: 1430-4171 (electronic version)
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,
funcao@fct.unesp.br
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
(*) Corresponding author. (E-mail: funcao@fct.unesp.br)
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