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Article

An Exploration of a Photochemical Pericyclic Reaction Using NMR Data

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Sara M. Hein

Department of Chemistry, Winona State University, Winona, MN 55987

J. Chem. Educ., 2006, 83 (6), p 940

DOI: 10.1021/ed083p940

Publication Date (Web): June 1, 2006

Section:

History, Education, and Documentation

Abstract

This inexpensive, small-scale experiment for advanced organic students describes the unambiguous identification of a photochemical dimerization product from eleven possible candidates. Trans-cinnamic acid is photochemically converted to a dimer product. This pericyclic reaction is analyzed through synthesis and derivatization, NMR spectroscopy, and molecular modeling techniques. Without referring to melting points in the literature or published spectra, students examine the identity of the product determined through careful study of the allowed mechanism. The orientation of orbital symmetries of each candidate is studied to find which one fits the allowed cycloaddition reaction as determined through molecular modeling studies and NMR spectral analysis. To help rule out other candidates, the product is esterified and acetylated. Students performing this experiment should previously had sophomore-level organic chemistry. In addition, they should have basic knowledge of pericyclic reactions and theory. The syntheses of the product and derivatives can be isolated in good yield. Students will be challenged to think critically about the possible outcomes, leading to the identification of the product.