Question about which oxygen acts as a nucleophile

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In summary, the conversation discusses the possibility of a protonated carbonyl mechanism involving nucleophilic attack by a -COOH group. There is some confusion about the equivalence of oxygens in the carboxylate anion and the protonated version. The correct mechanism involves resonance structures and does not involve the movement of protons.
  • #1
JHUK
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I posted in picture format to post on another website, but haven't found a reply yet:

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  • #2
How long ago did you post the other question - seems to me that this was posted whilst a vast majority of PFers were asleep, perhaps this is the issue with your other question.

However, by analogy with other reactions of the carbonyl group I'd think this is likely to involve effectively internal attack on the C=O by the COH, and work from there. Proton transfer, however is fairly rapid so the two mechanisms are pretty identical. Whether a kinetic isotope effect may be present in pure deuterated acid, I don't know.
 
  • #3
You're question is a little unclear because the mechanism shows nucleophilic attack by a -COOH group. The oxygens in these groups are actually equivalent and are best represented by resonance structures where the hydroxyl and carbonyl oxygens exchange.
 
  • #4
I was able to find an answer - the protonated carbonyl is the correct mechanism for both (the second is a mistake). You can see why by considering resonance.
 
  • #5
Yanick said:
You're question is a little unclear because the mechanism shows nucleophilic attack by a -COOH group. The oxygens in these groups are actually equivalent and are best represented by resonance structures where the hydroxyl and carbonyl oxygens exchange.

No, they are equivalent in the carboxylate anion, but not in the protonated version. Resonance structures do not involve the movement of protons.
 
  • #6
sjb-2812 said:
No, they are equivalent in the carboxylate anion, but not in the protonated version. Resonance structures do not involve the movement of protons.

You are correct sir. I shouldn't be answering questions when I'm dead tired.
 

Related to Question about which oxygen acts as a nucleophile

1. How does oxygen act as a nucleophile?

Oxygen can act as a nucleophile by donating a lone pair of electrons to a positively charged or electron deficient atom, forming a covalent bond. This allows oxygen to participate in chemical reactions and bond with other atoms.

2. What is a nucleophile?

A nucleophile is an atom or molecule that has a high electron density and is able to donate a pair of electrons to form a new covalent bond. Nucleophiles are commonly involved in chemical reactions and can bond with electrophiles, which are atoms or molecules with a low electron density.

3. How does oxygen's electronegativity affect its nucleophilicity?

Oxygen's electronegativity, or its ability to attract electrons, makes it a strong nucleophile. This is because oxygen's high electronegativity causes it to have a high electron density, making it more likely to donate a pair of electrons to form a covalent bond.

4. Can oxygen act as a nucleophile in both polar and nonpolar solvents?

Yes, oxygen can act as a nucleophile in both polar and nonpolar solvents. In polar solvents, oxygen's high electronegativity allows it to interact with other polar molecules and participate in reactions. In nonpolar solvents, oxygen can still donate a pair of electrons to form a bond with another atom or molecule.

5. What are some common reactions in which oxygen acts as a nucleophile?

Oxygen can act as a nucleophile in many different types of reactions, such as nucleophilic substitution, nucleophilic addition, and nucleophilic acyl substitution. Some common examples include the addition of water to an alkene to form an alcohol, the substitution of a leaving group with an alcohol in an SN2 reaction, and the addition of a nucleophile to a carbonyl group in an acyl substitution reaction.

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