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  Home > JCE Print > Journal of Chemical Education > Issues > 2001  > February  >
In the Laboratory
Influence of Dielectric Constant on the Spectral Behavior of Pinacyanol. A Spectrophotometric Experiment for Physical Chemistry
Raimon Sabaté, Llúcia Freire, and Joan Estelrich
Departament de Fisicoquímica, Universitat de Barcelona, Avda. Joan XXIII, s/n , E-08028 Barcelona, Spain
Cover
February 2001
Vol. 78 No. 2
p. 243
Abstract
The spectral behavior of pinacyanol was studied in methanol-water mixtures to observe the influence of the polarity of the solvent on wavelengths of maximal absorption and on the corresponding absorbance. The aqueous spectrum of pinacyanol shows two main peaks, which shift slightly toward longer wavelengths when the polarity of the solvent drops. In addition, a marked increase in the absorbance of one of the peaks concomitant to the reduction of solvent polarity is observed. This behavior is consistent with an n Æ p* transition. This laboratory experiment allows us to introduce and discuss the concepts of bathochromic and hypsochromic shift, as well as hyperchromic and hypochromic effects, and it can be completed by students in one 2-hour laboratory period.
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A handout for students and background notes for the instructor are available.
*  Contents JCE2001p0243W.doc (MS Word 97, Windows); JCE2001p0243W.pdf (Acrobat 4.0)
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*  Citation
 Sabaté, Raimon; Freire, Llúcia; Estelrich, Joan. J. Chem. Educ. 2001 78 243.
*  Keywords
 Dyes; Laboratory Instruction; Physical Chemistry; Solutions / Solvents; UV-Vis Spectroscopy
*  History
 Created:
Last Updated:		 December 22, 2000
August 31, 2005
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