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Question 22.2: Identify the following monosaccharides as (a) D-ribose or L-...

Identify the following monosaccharides as (a) D-ribose or L-ribose, (b) D-mannose or L-mannose.

(a)       (b)

ANALYSIS To identify D or L isomers, you must check the location of the  — OH group on the chiral carbon atom farthest from the carbonyl group. In a Fischer projection, this is the carbon atom above the bottom one. The  — OH group points left in an L enantiomer and right in a D enantiomer.

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In (a) the  — OH group on the chiral carbon above the bottom of the structure points to the right, so this is D-ribose. In (b) this  — OH group points to the left, so this is L-mannose.

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