Carbohydrates Video Carbohydrates or saccharides saccharo is Greek

Carbohydrates

• Video

• Carbohydrates, or saccharides (saccharo is Greek for ―sugar) are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. the empirical formula Cn(CH 2 O)n

Classifying carbohyrates w Monosaccharides contain 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).

• Oligosaccharides contain from 3 to 10 monosaccharide units (e. g. , raffinose). w. Polysaccharides 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).

Monosaccharides Aldoses (e. g. , glucose) have Ketoses (e. g. , fructose) have an aldehyde group at one end. a keto group, usually at C 2.

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.

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

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 2 n, 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).

2 n 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 2 n possible stereoisomers.