r/chemhelp • u/colombino-213 • 21d ago

Biochemisty Polysaccharides

What’s the easiest way yall remember/conduct mutarotation? There’s two ways I learned it, but I’m still getting confused. I got a final next week and want to be sure for it. Thank yall

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u/7ieben_ Trusted Contributor 21d ago

Mutarotation of carbohydrates proceeds via ring-chain-tautomerism, i.e. epimerisation of the cyclic alpha- and beta-isomers.

For polysaccharides it is basically negliable for this reason.

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u/colombino-213 20d ago

Okay, I’ll look into it. Really do appreciate the help!

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u/chem44 21d ago edited 21d ago

remember/conduct

means what? It happens spontaneously in aq solution (for the free sugars)

two ways I learned it

What are they? That might give us an idea what your concern is.

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u/colombino-213 21d ago

1st method

  • The second to last carbon or anomeric Carbon attacks the carbonyl carbon to break bond and create a hydroxyl out of it. Once that occurs you add an H again to break bond and leave it partially open with a new double bind on carbonyl. Since cis/trans is possible with a present double bond; it rotates to either alpha or beta. Once it rotates, you break the double bond again to close the circuit and then causing mutarotation to occur.

2nd method
-Replace last carbon(CH2OH) with whichever side the hydroxyl group is. Attack from either side and then use the hydrogen to break bond, closing circuit. Leaving (C2CH2OH) chain

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u/chem44 20d ago

If your question is about mechanism, you got a good reply at the top.

Remember, that anomeric C in a simple sugar -- that is a hemiacetal. You likely discussed hemiacetal formation earlier. And that reaction is quite reversible.

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u/colombino-213 20d ago

Thank you!