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  Home > JCE Print > Journal of Chemical Education > Issues > 2008  > September  >
In the Laboratory
The Laser Synthesis of Linear Polyynes: The Particle in a Box Revisited
Bruce D. Anderson and Christopher M. Gordon
Department of Chemistry, Muhlenberg College, Allentown, PA 18104
Cover
September 2008
Vol. 85 No. 9
p. 1279

Abstract
In this experiment, linear polyynes are synthesized and then the predictions of a one-dimensional, particle in a box are used to calculate the quantum mechanical box length for the polyynes. A solution of graphite in ethanol is irradiated with a Nd:YAG laser (532 nm) and the resulting solution is filtered and analyzed. Data from gas chromatography–mass spectrometry shows that linear polyynes, C6H2 and C8H2, are produced. The absorbance spectrum of the reaction mixture is obtained and the wavelengths are used to calculate the length of the conjugated pi system for each polyyne. The calculated box lengths for C6H2 and C8H2 are 9.23 Å and 10.82 Å, respectively. Although these values differ (47% and 22% larger) from the molecular lengths determined from the summation of bond lengths and from molecular modeling software, the experiment provides students with an opportunity to enrich their understanding of the predictions and limitations of the one-dimensional, particle in a box. The experiment is suitable for inclusion in a standard physical chemistry course or other upper-level laboratory where the principles of quantum mechanics are studied.
Supplement
Student handouts; Instructor notes
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Citation
Anderson, Bruce D.; Gordon, Christopher M. J. Chem. Educ. 2008, 85, 1279.
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Keywords
Alkenes; Computer-Based Learning; Hands-On Learning / Manipulatives; Laboratory Instruction; Lasers; Mass Spectrometry; Physical Chemistry; Quantum Chemistry; Synthesis; Upper-Division Undergraduate; UV-Vis Spectroscopy
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History
Created:
Last Updated:
8/4/2008
8/4/2008
 Caution! 
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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