215F07-notes-11-7-07-carbs1 - Chem 215 F07 Notes Dr Masato...

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Chem 215 F07 Notes – Dr. Masato Koreeda - Page 1 of 6. Date: November 7, 2007 Chapters 14.8; 23-1, 2, 5, and 7: Carbohydrates Carbohydrate nomenclature: Carbohydrates: • Polyhydroxylated aldehydes and ketones and their equivalents • Important constituents of both plants and animals D -glucose: The primary source of energy in the human body (CHOH)n CH 2 OH O H e.g., Hexoses: Sugars possessing six carbon atoms. • Pentoses: Sugars possessing five carbon atoms. • Aldoses: Sugars containing an aldehyde group. • Ketoses: Sugars containing a ketone group. • Monosaccharides: Carbohydrates that do not undergo cleavage on hydrolysis (treatment with water) to smaller molecules. I. Stereochemistry O H HO H HO H H HO H OH OH OH H HO H HO H H HO H O OH O OH HO H HO H H HO H H OH equatorial anomeric carbon axial 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 anomeric carbon opn-chain form of D -glucose another hemiacetal form of D -glucose one hemiacetal form of D -glucose These are anomers and (C-1) epimers. Glucose reacts like an aldehyde since small amounts of the open-chain form are present at equilibrium. Glucose has 4 stereocenters 2 4 = 16 stereoisomers possible 8 pairs of enantiomers (1) Fischer projection formulas (a) (+)-Glyceraldehyde: configurational reference compound for all monosaccharides H OH CH 2 OH O H D - (+)-glyceraldehyde vertical bonds go in and horizontal bonds come out small upper-case D configurational designation sign of optical rotation at the sodium D-line (589 nm) C H OH CH 2 OH O H C HO H O H CH 2 OH R R - (+)-glyceraldehyde This stereochemistry is defined as " D " if the OH is projected to the right. S -(-)-Glyceraldehyde has an L -configuration. D -Stereochemistry and the sign of optical rotation have no direct correlation, although many D sugars are dextrorotatory ( d or +).
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Chem 215 F07 Notes – Dr. Masato Koreeda - Page 2 of 6. Date: November 7, 2007 I. Stereochemistry (1) Fischer projection (cont’d) The configurational relatioship was established between D -glyceraldehyde and the naturally occurring positive-rotating grape sugar, (+)-glucose. HO H HO OH HO OH O 1 2 3 4 5 6 D HO OH HO OH HO O 1 2 3 4 5 6 D HO H HO OH O 1 2 3 4 5 D D -glucose D -fructose (found in many fruits) D -2-deoxyribose (found in DNA) [an aldohexose] [a ketohexose] [a deoxyaldopentose] (in its open-chain
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