Carbohydrates: Anomers, Mutarotation and the Glycosidic Bond · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Rings, anomers and sweet links

Science · Chemistry · ages 21-22
Name ______________________   Date ____________

  1. What is the anomeric carbon?

    • Any carbon with two hydroxyl groups
    • The former carbonyl carbon bonded to the ring oxygen and a new OH
    • The carbon most distant from the carbonyl

  2. How does glucose close from its open chain form?

    • The C5 hydroxyl attacks the aldehyde carbon to form a pyranose ring
    • Two sugars join and lose water
    • The chain is hydrolysed by acid

  3. What is mutarotation?

    • Formation of a glycosidic bond with loss of water
    • Hydrolysis of starch in acid
    • Interconversion of alpha and beta anomers through the open form

  4. A glycosidic bond survives basic storage yet breaks in stomach acid. Why?

    • It is an acetal that resists base but hydrolyses in acid
    • It is an ester that base cannot touch
    • It is a free anomeric centre

  5. At equilibrium, which glucose anomer dominates and why?

    • Alpha, since axial OH is stable
    • Beta, since its OH sits equatorial
    • Both equally, since the ring never opens

  6. Maltose reduces mild oxidants while sucrose does not.

    Circle one:   True   False

  7. Glycosidic bonds are esters that survive acid but break in base.

    Circle one:   True   False

  8. You test an unknown disaccharide and it does not reduce Benedicts reagent. What do you conclude?

    • It has a free anomeric centre
    • It must be a monosaccharide
    • Both anomeric centres are locked in glycosidic bonds
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Rings, anomers and sweet links W1-mt_XpSBU8b0HN-s1

  1. The former carbonyl carbon bonded to the ring oxygen and a new OH · Its configuration defines the alpha and beta anomers.
  2. The C5 hydroxyl attacks the aldehyde carbon to form a pyranose ring · Intramolecular attack builds a cyclic hemiacetal with a new stereocentre.
  3. Interconversion of alpha and beta anomers through the open form · Ring opening and reclosing lets the two anomers equilibrate.
  4. It is an acetal that resists base but hydrolyses in acid · Acetal identity explains base stability and acid cleavage.
  5. Beta, since its OH sits equatorial · Beta avoids strain by placing its anomeric OH equatorial.
  6. True · Maltose keeps a free anomeric centre, while sucrose locks both centres.
  7. False · They are acetals, so the opposite holds: stable to base, cleaved by acid.
  8. Both anomeric centres are locked in glycosidic bonds · No free centre means it cannot open to the aldehyde form.
Worksheet · LightMySky