1 Carbohydrates Classification Monosaccharides Chiral Carbon Atoms Structures of Important Monosaccharides Cyclic Structures

2 Carbohydrates Major source of energy from our diet Composed of the elements C, H and O Produced by photosynthesis in plants

3 Types of Carbohydrates Monosacchrides Disaccharides Contain 2 monosacchride units Polysacchrides Contain many monosacchride units

4 Monosacchrides Three Carbons = Triose Four Carbons = Tetrose Five Carbons = Pentose Six Carbons = Hexose

5 Monosacchrides Aldoses are monosacchrides with an aldehyde group and many hydroxyl (-OH) groups. Ketoses are monosacchrides with a ketone group and many hydroxyl (-OH) groups.

6 Learning Check C1 Identify each as tetrose, pentose or hexose, and as aldose or ketose A B

7 Solution C1 AB aldose, hexose ketose, pentose

8 Chiral Objects Chiral compounds have the same number of atoms arranged differently in space. A chiral carbon atom has four different groups attached

9 Mirror Images The three-dimensional structure of a chiral compound has a mirror image. Your hands are chiral. Try to superimpose your thumbs, palms, back of hands, and little fingers. Is it possible? Why or why not?

10 Learning Check C2 Determine if there is a chiral carbon in each compound. A B

11 Solution C2 A Yes, 4 different B No, the groups are attached 2 H atoms to the second C atom are identical

12 D and L Notation D,L tells which of the two chiral isomers we are referring to. If the –OH group on the next to the bottom carbon atom points to the right, the isomer is a D-isomer; if it points left, the isomer is L. The D form is usually the isomer found in nature.

13 D notation

14 Glucose

15 Fructose

16 Galactose D-galactose

17 Cyclic Structures Monosaccharides with 5-6 carbon atoms form cyclic structures The hydroxyl group on C-5 reacts with the aldehyde group or ketone group

18 Haworth Structure for D-Isomers The cyclic structure of a D-isomer has the final CH 2 OH group located above the ring.

19 Haworth Structure for D- Glucose Write –OH groups on the right (C2, C4) up Write –OH groups on the left (C3) down The new –OH on C1 has two possibilites: down for  anomer, up for  anomer

20 Haworth Structure for D- Glucose  -D-Glucose  -D-Glucose  

21 Mutarotation Mutarotation: A small amount of open chain is in equilibrium with the cyclic forms. The most stable form of glucose is β-D- glucose.  -D-glucose D-glucose (open) β-D-glucose (36%) (trace) (64%)

22 Learning Check C3 Write the cyclic form of  -D-galactose

23 Solution C3  -D-galactose