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Carbohydrates. Classification Monosaccharides Chiral Carbon Atoms Structures of Important Monosaccharides Cyclic Structures. Carbohydrates. Major source of energy from our diet Composed of the elements C, H and O Produced by photosynthesis in plants . Types of Carbohydrates.
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Carbohydrates Classification Monosaccharides Chiral Carbon Atoms Structures of Important Monosaccharides Cyclic Structures
Carbohydrates • Major source of energy from our diet • Composed of the elements C, H and O • Produced by photosynthesis in plants
Types of Carbohydrates • Monosacchrides • Disaccharides Contain 2 monosacchride units • Polysacchrides Contain many monosacchride units
Monosacchrides • Three Carbons = Triose • Four Carbons = Tetrose • Five Carbons = Pentose • Six Carbons = Hexose
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.
Learning Check C1 Identify each as tetrose, pentose or hexose, and as aldose or ketose A B
Solution C1 A B aldose, hexose ketose, pentose
Chiral Objects • Chiral compounds have the same number of atoms arranged differently in space. • A chiral carbon atom has four different groups attached
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?
Learning Check C2 Determine if there is a chiral carbon in each compound. A B
Solution C2 A Yes, 4 different B No, the groups are attached 2 H atoms to the second C atom are identical
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.
Galactose D-galactose
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
Haworth Structure for D-Isomers The cyclic structure of a D-isomer has the final CH2OH group located above the ring.
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
Haworth Structure for D-Glucose -D-Glucose-D-Glucose
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%)
Learning Check C3 Write the cyclic form of -D-galactose
Solution C3 -D-galactose