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The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 20 (2015) pp 13-20

Variation of the Conjugated Dye Experiment: Extent of Conjugation for a Linear p-system

Matthew G. Marmorino*,† and Tracy Huggins

Department of Chemistry and Biochemistry, Indiana University South Bend, 1700 Mishawaka Ave., South Bend, IN, 46634,; Department of Mathematical Sciences and Department of Physics and Astronomy, Indiana University South Bend, 1700 Mishawaka Ave., South Bend, IN, 46634
Received September 23, 2014. Accepted November 18, 2014.

Published: 30 January 2015

Abstract. The “conjugated dye” experiment has been in the physical chemistry curriculum for decades and modifications to it are well-known. In this article we change the analysis from an investigation of the length of the p-system in the compound to a determination of the amount of conjugation or delocalization of the p-electrons. It is shown that for linear polyenes (such as 2,4-hexadiene and 1,4-diphenyl-1,3-butadiene) the traditional application of the particle-in-a-box (PB) model and Hückel molecular orbital (HMO) methods is poor because of the lack of conjugation despite the alternation of double and single bonds that dominate the molecules. A perturbation to the PB model and a relaxation of simplifications in HMO theory allow these molecules to be studied and the amount of conjugation to be quantified.

Key Words: Laboratories and Demonstrations; physical chemistry; quantum

(*) Corresponding author. (E-mail:

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