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BIO NMDCAT Carbohydrates
nmdcat.online June 27, 2026

The reason that a freshly prepared solution of α-D-glucose has a different optical rotation from an equilibrium mixture is that mutarotation has not yet established the equilibrium between the α and β anomers. The open-chain form is a necessary intermediate in this process, and its concentration at equilibrium is extremely low (less than 0.1%) because

A. It is highly unstable and is rapidly oxidized to an acid
B. The cyclic hemiacetal form is significantly more thermodynamically stable than the open-chain aldehyde form
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C. It precipitates out of solution due to its low solubility
D. It is immediately fermented by airborne bacteria

📝 Explanation

The cyclic form, a hemiacetal, is much lower in energy than the free aldehyde. The equilibrium thus lies heavily on the side of the cyclic forms. The open form is a high-energy, transient intermediate that exists only briefly to allow anomeric interconversion.

📖 Additional Information

  • It is highly unstable and is rapidly oxidized to an acid
  • The cyclic hemiacetal form is significantly more thermodynamically stable than the open-chain aldehyde form
  • It precipitates out of solution due to its low solubility
  • It is immediately fermented by airborne bacteria

The cyclic form, a hemiacetal, is much lower in energy than the free aldehyde. The equilibrium thus lies heavily on the side of the cyclic forms. The open form is a high-energy, transient intermediate that exists only briefly to allow anomeric interconversion.

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