An Informative Model of Haworth Structures Although Haworth projections are not accurate representations of three-dimensional molecular structures, they are a convenient and popular manner in which to depict carbohydrates. However, many students become confused when they are required to manipulate these structures. This difficulty first arises in understanding the Haworth structure of sucrose. In most texts the fructose molecule is flipped to link the carbon #1 of glucose with the earban #2 of fructose to form the sucrose disaccharide. In this structure the glucose is in the alpha configuration while the fructose is in the beta conf~guration.The following exercise gives experience manipulating these structures and has been papular with most students. On a 3 x 5 notecard draw a large pyranose ring outline of glucose, leaving out the -OH, H, and carbon #6 -CHzOH. Use a heavy marker so that the image shows through to the other side of the card. Turn the card over and trace this structure on the reverse side. Do the same for the furanose ring structure of fructose on a separate notecard. Numher the carbon atoms on each side of both notecards appropriately. Using a pin, make a small hole at each carbon atom of the outlines. Take round tooth picks and darken one end with a marker to represent an -OH group . . with the undarkened end wpresmtmg the -11 arom. Ih thrrr toothpicks u w another culur marker tor small marahmnllows to rcprrscnt the -CH?OH group, usinz etthar -H. or -OH fur the other end aa nwded. Insert the tuothpirks in the holes of the natecard outlines with the proper orientation. Now the fructose can he flipped and the #1 carbon of glucose linked alpha to the #2 carbon of fructose (beta) by simply holding or taping. Most students have indicated that this exercise is extremely helpful in understanding Haworth projections.
H. Alan Rowe Norfolk State University Notfolk. VA 23504
Volume 71 Number 2 February 1994
131
