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ERIC Number: EJ820283
Record Type: Journal
Publication Date: 2006-Jul
Pages: 3
Abstractor: As Provided
Reference Count: 16
ISSN: ISSN-0021-9584
Usnic Acid and the Intramolecular Hydrogen Bond: A Computational Experiment for the Organic Laboratory
Green, Thomas K.; Lane, Charles A.
Journal of Chemical Education, v83 n7 p1046-1048 Jul 2006
A computational experiment is described for the organic chemistry laboratory that allows students to estimate the relative strengths of the intramolecular hydrogen bonds of usnic and isousnic acids, two related lichen secondary metabolites. Students first extract and purify usnic acid from common lichens and obtain [superscript 1]H NMR and IR spectra. The [superscript 1]H NMR spectrum reveals three downfield singlets at 11.1, 13.3, and 18.9 ppm, which correspond to three intramolecular hydrogen bonds. The IR spectrum additionally reveals three carbonyl stretching frequencies, which represent the hydrogen bond acceptors in usnic acid. The AM1 semi-empirical method is then employed to calculate (i) the heats of hydrogen bond formation, (ii) the atomic charges on the bridging hydrogens, (iii) the bond lengths of the acceptor carbonyl groups, and (iv) carbonyl IR stretching frequencies. The computed properties are then correlated to NMR and IR spectroscopic properties to reinforce fundamental concepts of the hydrogen bond. (Contains 3 figures and 1 table.)
Division of Chemical Education of the American Chemical Society. Subscription Department, P.O. Box 1267, Bellmawr, NJ 08099-1267. Tel: 800-691-9846; Tel: 856-931-5825; Fax: 856-931-4115; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education; Postsecondary Education
Audience: Students; Teachers
Language: English
Sponsor: N/A
Authoring Institution: N/A