The reference compound shown is a triose. Structures A to D are the four D-aldopentoses. Each is oxidised with hot dilute HNO3 to the aldaric (dicarboxylic) acid. Which give an optically inactive product?

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The reference compound shown is a triose. Structures A to D are the four D-aldopentoses. Each is oxidised with hot dilute $HNO X_{3}$ to the aldaric (dicarboxylic) acid. Which give an optically inactive product?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: A, C

HNO3 converts both CHO and CH2OH into COOH, giving a dicarboxylic acid whose two ends are identical. If the stereocentres are mirror-related the acid is meso. This happens for D-ribose (A) and D-xylose (C) (checked by comparing each acid with its mirror image), whereas D-arabinose and D-lyxose give optically active acids.

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The reference compound shown is a triose. Structures A to D are the four D-aldopentoses. Each is oxidised with hot dilute HNOX3​ to the aldaric (dicarboxylic) acid. Which give an optically inactive product?

Answer: A, C

More questions on Monosaccharide classification from drawn structures

The reference compound shown is a triose. Structures A to D are the four D-aldopentoses. Each is oxidised with hot dilute $HNO X_{3}$ to the aldaric (dicarboxylic) acid. Which give an optically inactive product?