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The Chemical Educator
ISSN: 1430-4171 (electronic version)
Abstract Volume 23
(2018) pp 169-173
A Laboratory Experiment for Illustrating the Kinetic Isotope Effect
Pauline Lebrun, Alice Kirk, Andrew McStay, and Arno Kraft*
Institute of Chemical Sciences, School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom, A.Kraft@hw.ac.uk
Received June 25, 2018. Accepted July 24, 2018.
Published: 12 August 2018
Abstract. This paper describes the study of the kinetic isotope effect for the reaction between cyclohexanone and iodine under acidic conditions that has been adapted for an advanced level undergraduate organic chemistry laboratory class. The kinetics of the reaction of iodine with cyclohexanone can be readily followed with a UV-Vis spectrophotometer or even a home-built colorimeter. The results are compared with the reaction of iodine with cyclohexanone-d4, a deuterated analog which students prepare by a simple and cheap deuteration. The deuterated cyclohexanone reacts more slowly than the non-deuterated cyclohexanone by a factor of 3.5 ± 1.2, which confirms that a C-H bond is broken in the rate-determining step and illustrates a primary kinetic isotope effect.
Key Words: Laboratories and Demonstrations; physical organic chemistry; kinetic isotope effect; halogenation of ketones; active learning
(*) Corresponding author. (E-mail: A.Kraft@hw.ac.uk)
Article in PDF format (328 KB) HTML format
Supporting Materials:
Detailed reagent list, student handout, instructor notes,
analytical data for deuterated cyclohexanone, a summary of student results, a
calculation to estimate the reaction time, instructions for making a
colorimeter, Arduino code for following the kinetics, and typical results.
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