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Monosaccharides - Wohl Degradation quiz

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  • What is the main purpose of the Wohl degradation reaction in carbohydrate chemistry?
    Wohl degradation is used to shorten the carbon chain of an aldose by one carbon per cycle, opposite to the Kiliani-Fischer chain lengthening.
  • How does the stereochemistry of the sugar change during Wohl degradation?
    The stereochemistry at all chiral centers is retained except for the C2 position, which becomes achiral after the reaction.
  • What is the first step in the Wohl degradation of D-glucose?
    The first step is converting D-glucose into an oxime by reacting it with hydroxylamine.
  • What reagent is used to convert the oxime into a cyanohydrin in Wohl degradation?
    An anhydride is used to dehydrate the oxime and rearrange it into a cyanohydrin via the Beckman rearrangement.
  • What happens to the cyanohydrin in the third step of Wohl degradation?
    The cyanohydrin is treated with a strong base, usually methoxide, to reform the carbonyl and eliminate the cyanohydrin, shortening the chain by one carbon.
  • What type of elimination occurs during the removal of the cyanohydrin in Wohl degradation?
    An alpha elimination occurs, where two single bonds are replaced by a double bond on the same carbon.
  • What is the final product of Wohl degradation when starting from D-glucose?
    The final product is D-arabinose, a monosaccharide with retained chirality at all chiral centers except the new aldehyde at C2.
  • How does Wohl degradation differ from Kiliani-Fischer synthesis in terms of epimer formation?
    Wohl degradation produces a single epimer product with specific stereochemistry, unlike Kiliani-Fischer which can create multiple epimers.
  • Why can multiple sugars produce the same product in Wohl degradation?
    Because the C2 position becomes achiral after the reaction, different C2 epimers can yield the same final product.
  • What functional group is lost from the sugar during Wohl degradation?
    A cyanohydrin group (HCN) is eliminated, resulting in the loss of the top carbon from the sugar.
  • What is the role of hydroxylamine in Wohl degradation?
    Hydroxylamine reacts with the aldehyde group to form an oxime, which is a type of imine derivative.
  • What is the specific name for the imine derivative formed from hydroxylamine and an aldehyde?
    The imine derivative formed is called an oxime.
  • What happens to the C2 carbon during Wohl degradation?
    The C2 carbon, originally chiral, becomes an aldehyde and loses its chirality after the reaction.
  • What is the significance of the alpha elimination in Wohl degradation?
    Alpha elimination replaces two single bonds with a double bond on the same carbon, facilitating the removal of the cyanohydrin.
  • How does the chain length of a monosaccharide change after one cycle of Wohl degradation?
    The chain length is shortened by one carbon, and this process can be repeated until no more alcohol groups remain.