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In the Laboratory
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Quantitative Determination of the Rotameric Energy Differences of 1,2-Dihaloethanes Using Raman Spectroscopy. An Experimental Project for the Physical Chemistry Laboratory
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Mark D. Young, Natalia C. Borjemscaia, and Brian D. Wladkowski
Department of Chemistry, McDaniel College, Westminster, MD 21157
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June 2005
Vol. 82 No. 6
p. 912
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| Abstract |
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The effects of structure and environment on the rotameric energy difference between gauche and trans conformations of 1,2-disubtitutedethanes are determined quantitatively through the use of Raman spectroscopy. Two 1,2-dihaloethanes (chloro- and bromo-) were analyzed in the condensed phase (pure liquid, carbon tetrachloride, and acetonitrile solutions). Since the gauche conformation of these molecules has a nonzero dipole, dissolving the compounds in solvents with increasing dielectric constant causes a stabilization of the gauche conformation, thus decreasing the absolute energy difference between the rotamers. The major factor governing the intrinsic stability is that of steric hindrance. As the size of the halogen increases, more steric repulsion occurs, resulting in an increase in the absolute energy difference. Although in most cases steric hindrance was the dominant factor, 1,2-dichloroethane was found to favor the gauche conformation in both the pure liquid and acetonitrile solution, illustrating the importance of solvation effects.
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| Supplement |
Instructions for the students and notes for the instructor are available.
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 Contents |
JCE2005p0912W.doc (Microsoft Word)
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| More Information |
Citation |
Young, Mark D.; Borjemscaia, Natalia C.; Wladkowski, Brian D. J. Chem. Educ. 2005 82 912.
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Keywords |
Alkanes / Cycloalkanes; Conformational Analysis; Hands-On Learning / Manipulatives; Instrumental Methods; IR Spectroscopy; Laboratory Instruction; Physical Chemistry; Quantitative Analysis; Raman Spectroscopy; Stereochemistry; Upper-Division Undergraduate
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History |
Created:
Last Updated: |
April 27, 2005
May 6, 2005
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