February 22, 2024, 09:49:47 AM
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Topic: Nucleophilic attack to C having protonated OH or to proton of protonated OH  (Read 1969 times)

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Offline maimavi

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Hello everyone,

I have a question in mind. Sometimes I see nuclophile attacking the Carbon having protonated OH (OH2+) and water leaves as a leaving group. But sometimes, I see nucleophilic attack directly to hydrogen of protonated OH. What determines that? Is there a rule like weak nucleophiles cannot attack the Carbon atom so that attack to acidic hydrogen on protonated OH or something?

Offline orgopete

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These are two different types of reactions. One is kinetic and one is thermodynamic. Which is which? How will that effect the predicted products?
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline zsinger

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Not sure I understand?  Hydrogen is NOT being attacked, but rather is usually bound to a terminal oxygen (an alcohol).  Can you clarify?  Do you mean carbon being attacked?
              -Zack
"The answer is of zero significance if one cannot distinctly arrive at said place with an explanation"

Offline orgopete

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Not sure I understand?  Hydrogen is NOT being attacked, but rather is usually bound to a terminal oxygen (an alcohol).  Can you clarify?  Do you mean carbon being attacked?
              -Zack

If you draw out the poster's question, you can have the electrons of water attack the carbon or the hydrogen.

My point is it appears the poster is suggesting these are alternate pathways, a reaction occurs via one or the other. This is not correct. In order for the poster to understand these reactions, the poster needs to understand the difference. Also, I think this is only true for an SN1 reaction. I'm not aware of an SN2 reaction with water, not that it doesn't occur, just that I don't know. (Is this how 18O-ethanol is made?)
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline zsinger

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Nice one there Pete!  Learned something new today!
               -Z
"The answer is of zero significance if one cannot distinctly arrive at said place with an explanation"

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