Dolbier HW Solutions 630

Dolbier HW Solutions 630 - acid to be optically active. If...

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The structure of phlorizin is therefore 25.34 Consider all the individual pieces of information in the order in which they are presented. 1. Chain extension of the aldopentose ( 2 )-arabinose by way of the derived cyanohydrin gave a mixture of ( 1 )-glucose and ( 1 )-mannose. Chain extension of aldoses takes place at the aldehyde end of the chain. The aldehyde function of an aldopentose becomes C-2 of an aldohexose, which normally results in two carbohydrates diastereomeric at C-2. Thus, ( 1 )-glucose and ( 1 )-mannose have the same con f guration at C-3, C-4, and C-5; they have opposite con f gurations at C-2. The con f gu- ration at C-2, C-3, and C-4 of ( 2 )-arabinose is the same as that at C-3, C-4, and C-5 of ( 1 )- glucose and ( 1 )-mannose. 2. Oxidation of ( 2 )-arabinose with warm nitric acid gave an optically active aldaric acid. Because the hydroxyl group at C-4 of ( 2 )-arabinose is at the right in a Fischer projection formula (evidence of step 1), the hydroxyl at C-2 must be to the left in order for the aldaric
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Unformatted text preview: acid to be optically active. If the C-2 hydroxyl group had been to the right, an optically inactive meso aldaric acid would have been produced. Therefore we now know the con f gurations of C-3 and C-5 of ( 1 )-glucose and ( 1 )-mannose and that these two aldohexoses have opposite con f gurations at C-2, but the same (yet to be determined) con f guration at C-4. CHO CH 2 OH H H H HO OH CHOH OH 1 2 3 4 5 6 CHO CH 2 OH HO H H HO H CHOH OH 1 2 3 4 5 6 [One of these is ( 1 )-glucose, the other is ( 1 )-mannose.] CHO CH 2 OH H OH CHOH H OH 1 2 3 4 5 CO 2 H CO 2 H H CHOH OH H OH Achiral meso form; cannot be optically active HNO 3 CHO CH 2 OH H H CHOH HO OH 1 2 3 4 5 Partial stereostructure of ( 2 )-arabinose CO 2 H CO 2 H HO H CHOH H OH 1 2 3 4 5 Aldaric acid from ( 2 )-arabinose; optically active irrespective of configuration at C-3 HNO 3 CH 2 CH 2 OH CH 2 OH O HO HO O OH OH OH C O 724 CARBOHYDRATES...
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This note was uploaded on 10/03/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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