Use of Optical Rotation and NMR Signal Counting To Identify Common Aldoses

An inexpensive, small scale experiment for second semester organic students describes the unambiguous identification of a common aldose "unknown" from five possible candidates: glucose, mannose, galactose, arabinose, or xylose. The aldose is first reduced to an alditol to permit possible s...

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Bibliographic Details
Published in:Journal of chemical education 2004-05, Vol.81 (5), p.708
Main Author: Almy, John
Format: Article
Language:English
Subjects:
Carbohydrates
Chemistry
Identification
Laboratories
Molecular structure
NMR
Nuclear magnetic resonance
Optical communication
Optical properties
Optical rotation
Organic chemistry
Polarimetry
Science Experiments
Science Instruction
Scientific imaging
Teaching
Teaching Methods
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Description
Summary:An inexpensive, small scale experiment for second semester organic students describes the unambiguous identification of a common aldose "unknown" from five possible candidates: glucose, mannose, galactose, arabinose, or xylose. The aldose is first reduced to an alditol to permit possible symmetry in the molecule. The alditol is then converted to its peracetate for improved crystallization and analysis by polarimetry and NMR. Without referring to melting points in the literature or published spectra, students examine the symmetry properties of each candidate's alditol peracetate to determine which structure fits the rotational data and NMR spectra. As an option, the ketoses, sorbose and fructose, can be similarly reduced and acetylated. Each will produce peracetate mixtures that can be identified by NMR using the information obtained from the aldoses, again without the need for published data.
ISSN:0021-9584
1938-1328
DOI:10.1021/ed081p708