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Altius 7 COVID Question 19
Daniel_4987
#1 Posted : Monday, August 10, 2020 3:13:30 PM
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I have a question regarding Altius 7 COVID Question 19.

The question asks:
Dehydroascorbic acid is formed as the result of ascorbic acid undergoing:

a) carboxylation
b) hydrolysis
c) reduction
d) oxidation

(Sorry I attempted to attach a screenshot of the reaction but couldn't figure out how)

The correct answer is d) oxidation

I am confused however as H+ is a product of the reaction, which I assumed to mean that ascorbic acid lost (+) charge, gaining electrons and thus being reduced.

Can you let me know where I went wrong?

Thank you so much!
INSTR_Katerina_102
#2 Posted : Tuesday, August 11, 2020 1:43:51 AM
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Hi Daniel,

I am confused however as H+ is a product of the reaction, which I assumed to mean that ascorbic acid lost (+) charge, gaining electrons and thus being reduced.

I would not use H+ as an indicator of what is going on with a molecule, as molecules often exchange protons just to get certain mechanisms done. Proton transfer is a fast process and often doesn't tell you a lot about the reactivity (at least on the MCAT).

For this reaction, I have attached an example with the structures that I assume were provided.

https://alumniubcca-my.s...GYPSCcEMo4WWaQ?e=GVFG1F

Essentially what is going on when going from ascorbic acid to dehydroascorbic acid is that you are losing CH bonds and gaining CO bonds. By bonding to a more electronegative element (oxygen), the Cs in dehydroascorbate have less electron density, and thus are considered to be oxidized.

Please let me know if this is unclear,

Katt
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