Generation and Observation of the Cyclopentadienyl Anion: A Negatively Charged Aromatic Molecule

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 2 Issue 6 (1997), S1430-4171(97)06152-3

Generation and Observation of the Cyclopentadienyl Anion: A Negatively Charged Aromatic Molecule

Gary W. Breton

Berry College, Mount Berry, GA 30149-5016

Published online: 24 December 1997

Abstract. The study of charged aromatic species greatly enhances discussions of the theory of aromaticity. The conveniently low acidity of cyclopentadiene (pK_a = 15) affords the opportunity to generate the aromatic cyclopentadienyl anion in an organic laboratory class. This experiment describes the preparation of a solution of deuterated dimethylsulfinyl anion in an NMR tube, followed by the addition of freshly prepared cyclopentadiene. The ¹H NMR spectrum of the resulting aromatic anion is compared with that of the isoelectronic (but uncharged) benzene, and contrasted with the spectra of several nonaromatic and antiaromatic compounds. Treatment of the anion with an equivalent of trifluoroacetic acid quantitatively affords cyclopentadiene.

Key Words: Laboratories and Demonstrations; aromaticity; anion; cyclopentadiene; cyclopentadienyl anion; NMR

(*) Corresponding author. (E-mail: gbreton@berry.edu)

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Student Instructions (22 KB) 10.1007/s00897970152b