polarity question

[joonkimdds]

I am going over carboxylic acid in Kaplan blue book (page 409)
It says that protonating the O in carbonyl makes carbon more positive.
If O is protonated, it becomes less negative so how does this positive O make the C more positive, too?

O is more electronegative than C and so that the O has partial negative charge and C has partial positive charge.
If O becomes more positive, I think it should make C more negative charge.




By the way, which one is more electronegative between C and Cl?
I thought C is more electronegative because it's at the lower level and closer to the core.

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[joonkimdds]

bump~

 

[Jaylee777]

Carbonyl carbon is always partially positive making it susceptible to nucleophillic attack. Now when the carbonyl oxygen is protonated it has a positive formal charge. This isnt stable so in order to restabilize the oxygen it needs to regain its other lone pair. The lone pair comes from the double bond to the carbon...and in order to get the electrons to go on the oxygen, a nucleophile must attack the carbonyl carbon. By saying the carbon is more positive is just meaning that it is more susceptible to nucleophiles. Review a acid catalyzed carbonyl mechanism and that should make it clear.

 

[Flipper405]

By the way, which one is more electronegative between C and Cl?
I thought C is more electronegative because it's at the lower level and closer to the core.

Cl is more electronegative... by a lot. Only O and F are more electronegative than Cl.
http://en.wikipedia.org/wiki/Electronegativity