PracticeExam4_key - Name_KEY_ EID_ CH n339K Exam 4 8 July...

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Name________________ KEY _________________________ EID__________________________________________ 1 CH n339K Exam 4 8 July 2008 125 points total 10 pts. 1 . a . The sucrose substitute tagatose (see Fig. 7-3b, p. 237) is produced by hydrolyzing lactose and then chemically converting one of the two resulting aldoses to a ketose. Which monosaccharide residue of lactose gives rise to tagatose? Lactose is hydrolyzed to galactose + glucose (both aldoses). When these are chemcially converted to ketoses, the chiral center at C2 is lost, but the configurations at the other chiral centers (C3, C4, and C5) remain unchanged. Fig. 7-3, p. 237, you can see that tagatose shares the same configuration at C3, C4, and C5 as galactose, but not glucose. Thus, tagatose is derived from the galactose residue of lactose. 10 pts. b . Draw the Haworth projection of α -D-tagatose OH CH 2 OH H HOH 2 C H H HO OH O " -D-tagatose 2 . The values of the specific rotation, [ α ] 20 D , for the α and β anomers of D-galactose are 150.7° and 52.8°, respectively. A mixture that is 20% α -D-galactose and 80% β -D-galactose is dissolved in water at 20° C.
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This note was uploaded on 11/25/2009 for the course CH 53890 taught by Professor Raymonds during the Spring '09 term at University of Texas at Austin.

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PracticeExam4_key - Name_KEY_ EID_ CH n339K Exam 4 8 July...

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