Ch_322b_22.06

Ch_322b_22.06 - Some Problems with the Open-Chain (Fischer)...

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Some Problems with the Open-Chain (Fischer) Structure for D-(+)-Glucose CHO CH 2 OH OH OH OH HO H H H H the Fischer structure for D-(+)-glucose The open-chain aldose structure is not consistent with some of the chemical and physical properties of glucose. (1) Certain standard aldehyde reactions, such as bisulfite addition, do not occur. Also the Schiff reagent test (a color test based on the easy oxidation of the aldehyde function) fails. (2) D-(+)-Glucose obtained from a solution of water shows a mp of 147 o C (dec). This sample redissolved in water has an initial specific rotation of [ ! ] = +112 o . But over time, the specific rotation drops to [ ! ] = +52 o . This change in rotatory power is called mutarotation . A trace of acid or base accelerates mutarotation. (3) A second form of D-(+)-glucose can be isolated that shows an initial [ ! ] = +19 o in water. Over time, the specific rotation of this solution changes to [ ! ] = +52 o .
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The Cyclic Hemiacetal Structures These observations of the properties and behavior of D-(+)-glucose are not consistent with the simple aldose structure. It soon became
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_22.06 - Some Problems with the Open-Chain (Fischer)...

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