Chapter 15 Carbohydrates 15 3 Haworth Structures of

Chapter 15 Carbohydrates 15. 3 Haworth Structures of Monosaccharides General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1

Haworth Structures Haworth structures § are the prevalent form of monosaccharides with 5 or 6 carbon atoms § form when the hydroxyl group on carbon 5 (C 5) reacts with the aldehyde or ketone group General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 2

Haworth Structures (continued) Haworth structures § are cyclic hemiacetals § form when the C═O group and the —OH are part of the same molecule § of hexoses form when the —OH on C 5 reacts with a C═O group § of a D-isomer place the —CH 2 OH of C 6 above the ring General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 3

Guide to Drawing Haworth Structures General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 4

Drawing the Haworth Structures for Glucose STEP 1 Turn the open carbon chain clockwise by 90°. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 5

Drawing the Haworth Structures for Glucose (continued) STEP 2 Fold the carbon chain into a hexagon by: § moving C 5 (with C 6) above C 3 § bonding the C 5 —OH to C═O of C 1 § writing the —OH groups on C 2 and C 4 below the ring § writing the —OH group on C 3 above the ring § writing a new —OH on C 1 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6

Drawing the Haworth Structures for Glucose (continued) STEP 2 continued General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7

Drawing the Haworth Structures for Glucose (continued) STEP 3 The new —OH on C 1: § forms two isomers called anomers §is drawn down for the α anomer §Is drawn up for the β anomer General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 8

-D-Glucose and β-D-Glucose in Aqueous Solution When placed in an aqueous solution, § cyclic structures open and close § -D-glucose converts to β-D-glucose and back § there is only a small amount of open chain General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9

Haworth Structures of Fructose § is a ketohexose § forms Haworth structures when the —OH on C 5 bonds to the C═O on C 2 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 10

Learning Check Draw the Haworth structure of -D-galactose. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11

Solution STEP 1 Turn the open carbon chain clockwise by 90°. OH HO H H H General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 12

Solution (continued) STEP 2 Fold the carbon chain into a hexagon. HO HO H H General, Organic, and Biological Chemistry H OH Copyright © 2010 Pearson Education, Inc. 13

Solution (continued) STEP 3 Draw the new —OH on C 1 down for the anomer. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 14