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  Home > JCE Print > Journal of Chemical Education > Issues > 2006  > September  >
In the Laboratory
The Hammett Equation: Probing the Mechanism of Aromatic Semicarbazone Formation
Glenn K. Ikeda, Karen Jang, Scott O. C. Mundle, and Andrew P. Dicks
Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
Cover
September 2006
Vol. 83 No. 9
p. 1341

Abstract
An organic class project is described where upper-level undergraduates measure kinetic rate constants for semicarbazone formation, by reacting semicarbazide with a meta- or para-substituted benzaldehyde. UV-vis spectroscopy is used to follow product formation. Individual results are compiled to yield a class data set, which is used to construct a linear Hammett plot applying empirical σX values. Students determine the reaction ρ value and use it to elucidate the rate-determining step of the multistep mechanism. An opportunity exists to interpret the form and meaning of a concave-downwards Hammett plot from the literature.
Supplement
Theory underlying the Hammett equation, instructions for the students, and notes for the instructor are available.
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Citation
Ikeda, Glenn K.; Jang, Karen; Mundle, Scott O. C.; Dicks, Andrew P. J. Chem. Educ. 2006 83 1341.
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Keywords
Addition Reactions; Aldehydes / Ketones; Collaborative / Cooperative Learning; Hands-On Learning / Manipulatives; Kinetics; Laboratory Instruction; Mechanisms of Reactions; Organic Chemistry; Upper-Division Undergraduate; UV-Vis Spectroscopy
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History
Created:
Last Updated:
8/7/2006
8/18/2006
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Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
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