ORGANIC CHEMISTRY 354

THE STRUCTURE OF GLUCOSE

FISCHER PROJECTIONS

BASIC SUGAR REACTIONS

FISCHER'S STRUCTURE DETERMINATION
FISCHER PROJECTIONS

A WAY TO EASILY SHOW STEREOCHEMISTRY OF MOLECULES WITH MANY CHIRAL CENTERS.

REPRESENT A TETRAHEDRAL CARBON WITH TWO PERPENDICULAR LINES.

ROTATION RULES.

MORE RULES.

AN ASSIGNMENT.

CARBOHYDRATES (SACCHARIDES)

STRUCTURAL FRAMEWORK FOR PLANTS

SOURCE OF ENERGY FOR PLANTS AND ANIMALS

  • TABLE SUGAR
  • WOOD
  • COTTON
  • POTATOES
  • STARCH

FORMULA CnH2nOn or Cn(H2O)n

SIMPLE vs. COMPLEX SACCHARIDES

  • SIMPLE SACCHARIDE = GLUCOSE
  • DISACCHARIDE = SUCROSE (1 SUCROSE --> 1 GLUCOSE + 1 FRUCTOSE)
  • POLYSACCHARIDE = CELLULOSE (1 CELLULOSE --> ~3000 GLUCOSE)

GLUCOSE (C6H12O6) IS THE MOST COMMON MONOSACCHARIDE! WHAT IS ITS STRUCTURE?

1. C6H12O6, FORMULA

a. ONE SITE OF UNSATURATION: THEREFORE EITHER A RING, C=C, or C=O

b. LARGE NUMBER OF OXYGENS: THEREFORE MANY ALCOHOLS AND/OR ETHERS

2. REACTS WITH ONE MOLE OF PHENYLHYDRAZINE TO GIVE A SOLID PHENYLHYDRAZONE: THEREFORE C=O

3. C6H12O6 + Br2, H2O ---> C6H12O7 (A CARBOXYLIC ACID). BROMINE WATER ONLY OXIDIZES ALDEHYDES WITH AN ALPHA ELECTRON WITHDRAWING GROUP: THEREFORE, AN ALPHA HYDROXY OR ALPHA ETHER ALDEHYDE

4. C6H12O6 + HNO3 --> C6H10O8 (A DICARBOXYLIC ACID): THEREFORE, CONTAINS ONE PRIMARY ALCOHOL

5. C6H12O6 + ACETIC ANHYDRIDE --> C16H22O11 (A PENTAACETATE): THEREFORE, FIVE ALCOHOLS

6. C6H12O6 + H2 --> C6H14O6

7. C6H14O6 + ACETIC ANHYDRIDE --> C18H26O12 (A HEXAACETATE)

8. C6H12O6 + HI --> 2-IODOHEXANE: THEREFORE, ALL SIX CARBONS ARE IN A STRAIGHT CHAIN!

GLUCOSE IS 2,3,4,5,6-PENTAHYDROXYHEXANAL.

MONOSACCHARIDES ARE OPTICALLY ACTIVE POLYHYDROXY ALDEHYDES AND KETONES.

CLASSIFICATION OF MONOSACCHARIDES

BY NUMBER OF CARBONS

  • 6 CARBONS = HEXOSE
  • 5 CARBONS = PENTOSE
  • 4 CARBONS = TETROSE
  • 3 CARBONS = TRIOSE

BY FUNCTIONALITY

  • ALDEHYDE = ALDOSE
  • KETONE = KETOSE

COMBINED

  • ALDOHEXOSE
  • KETOHEXOSE
  • ALDOTETROSE, ETC.

BY STEREOCHEMISTRY

  • DRAW THE MONOSACCHARIDE AS A FISCHER PROJECTION IN A VERTICAL FASHION WITH THE OXIDIZED END ON TOP. IF THE HYDROXYL GROUP ON THE BOTTOM CHIRAL ATOM IS ON THE RIGHT, IT IS THE (D)-ISOMER.
  • IF ON THE LEFT, IT IS THE (L)-ISOMER.

EXAMPLES.

DETERMINE SUGAR CONFIGURATIONS BY EITHER

DEGRADATION, more, OR

SYNTHESIS

THE CONFIGURATION OF (+)-GLUCOSE, AN ALDOHEXOSE

1. (+)-GLUCOSE:

2. (+)-GLUCOSE:

    CAN BE DEGRADED TO D-GLYCERALDEHYDE.

3. (-)-ARABINOSE (AN ALDOPENTOSE):

    CAN BE CONVERTED TO TWO ALDOHEXOSES, (+)-GLUCOSE AND (+)-MANNOSE

4. (-)-ARBINOSE:

5. (+)-GLUCOSE AND (+)-MANNOSE:

6. (+)-GULOSE:

    GIVES THE SAME DIACID AS (+)-GLUCOSE WITH NITRIC ACID.

(+)-GLUCOSE CAN ONLY BE 3.

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