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Synthesis of Quinolines and Their Characterization by 2-D NMR Spectroscopy

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Abhijit Mitra and Ali Assarpour

Department of Chemistry and Biochemistry, Manhattan College, College of Mt. St. Vincent, Riverdale, NY 10471-4098

Pamela J. Seaton and R. Thomas Williamson

Department of Chemistry, University of North Carolina-Wilmington, Wilmington, NC 28403-3297

J. Chem. Educ., 2002, 79 (1), p 106

DOI: 10.1021/ed079p106

Publication Date (Web): January 1, 2002

Abstract

Most undergraduate laboratory courses incorporate the use of simple one-dimensional (1-D) NMR spectroscopy for structure elucidation. However, structure elucidation of methylquinolines by 1-D ¹H NMR spectroscopy using vicinal and long-range coupling constant values is inadequate for complete assignment. There are numerous other compounds whose structure cannot be adequately defined from their 1-D ¹H NMR spectra. With modern spectrometers it is now possible to do 2-D NMR experiments that are much more informative. The COSY is one of the most important experiments in 2-D NMR spectroscopy and is used for correlating the two spin systems of the quinoline rings and thus developing the connectivity of the hydrogen atoms.

Although methyl quinolines are commercially available, the synthesis of these compounds is pedagogically valuable. Quinolines can be synthesized from unknown methylanilines using the Skraup's synthesis. This involves a sequence of reactions starting with the Michael (1,4-) addition of the aniline nitrogen to propenal, followed by electrophilic aromatic substitution, and subsequent dehydration and oxidation to give quinoline.