Carbohydrates

1. Carbohydrates

2. Video

4. CarbohydratesCarbohydrates, or saccharides (saccharo is Greek for ―sugar) are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. the empirical formula Cn(CH2O)n

5. Classifying carbohyrates • Monosaccharidescontain a single polyhydroxy aldehyde or ketone unit (e.g., glucose, fructose). a monosaccharide is a triose, tetrose, pentose or hexose. • Disaccharides - Disaccharides consist of two monosaccharide units linked together by a covalent bond (e.g., sucrose).

6. OligosaccharidesOligosaccharides contain from 3 to 10 monosaccharide units (e.g., raffinose). • PolysaccharidesPolysaccharides contain very long chains of hundreds or thousands of monosaccharide units, which may be either in straight or branched chains (e.g., cellulose, glycogen, starch).

7. Monosaccharides Aldoses (e.g., glucose) have an aldehyde group at one end. Ketoses (e.g., fructose) have a keto group, usually at C2.

9. D vs L Designation D & L designations are based on the configuration about the single asymmetric C in glyceraldehyde. The lower representations are Fischer Projections.

10. Sugar Nomenclature For sugars with more than one chiral center, D or Lrefers to the asymmetric C farthest from the aldehyde or keto group. Most naturally occurring sugars are D isomers.

11. D & L sugars are mirror images of one another. They have the same name, e.g., D-glucose & L-glucose. Other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc. The number of stereoisomers is 2n, where n is the number of asymmetric centers. The 6-C aldoses have 4 asymmetric centers. Thus there are 16 stereoisomers (8 D-sugars and 8 L-sugars).

12. 2n Rule When a molecule has more than one chiral carbon, each carbon can possibly be arranged in either the right-hand or left-hand form, thus if there are n chiral carbons, there are 2n possible stereoisomers.