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 C_nH_2nO_n or C_n(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:

HAS FOUR CHIRAL CENTERS, THEREFORE THERE ARE 16 POSSIBLE STEREOISOMERS.

2. (+)-GLUCOSE:

CAN BE DEGRADED TO D-GLYCERALDEHYDE.

THERE ARE 8 D-(+)-GLUCOSE STEREOISOMERS.

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

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

(+)-GLUCOSE AND (+)-MANNOSE ARE MEMBERS OF ONE OF THE PAIRS 1 & 2, 3 & 4, 5 & 6, OR 7 & 8.

(-)-ARABINOSE IS 9, 10, 11, OR 12 .

4. (-)-ARBINOSE:

NITRIC ACID OXIDATION GIVES AN OPTICALLY ACTIVE DIACID.

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

BOTH GIVE OPTICALLY ACTIVE DIACIDS WITH NITRIC ACID.

REVIEW.

6. (+)-GULOSE:

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

HOW CAN TWO ALDOHEXOSES GIVE THE SAME DIACID?

(+)-GLUCOSE CAN ONLY BE 3.