2 questions with BR Orgo chapter on carbonyls

[UIUCstudent]

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The alpha hydorgen of a carbyonyl has a pKa of 19. On a passage would this be considered an acidic site?
Let's say a ethanoic acid as an example. Would this be considered a diprotic species?

Also, what does BR mean when it says "alkyl bromides and chlorides yield more O-akylation side products than akyl halides"? This is in relation to the carbanion doing a nucelophilic subsitution reaction on alkyl halid resulting in a longer ketone molecule. BR doesn't seem to expand on what O-akylation is.

 

[PeterPesto]

The alpha hydorgen of a carbyonyl has a pKa of 19. On a passage would this be considered an acidic site?
Let's say a ethanoic acid as an example. Would this be considered a diprotic species?

Also, what does BR mean when it says "alkyl bromides and chlorides yield more O-akylation side products than akyl halides"? This is in relation to the carbanion doing a nucelophilic subsitution reaction on alkyl halid resulting in a longer ketone molecule. BR doesn't seem to expand on what O-akylation is.

A pKa of 19 is a really weak acid. They are referring to the hydrogen attached to the alpha carbon. This weakly acidic nature allows for enolate chemistry. They are NOT referring to the acidic hydrogen attached to oxygen in a carboxylic acid. It would be a diprotic species in an EXTREMELY basic environment.

 

[UIUCstudent]

Alright. I just did a BR passage and lo and behold there was a question about this. The answer was only one acidic site..though I still think this is debatable. Thanks Peter.

Can someone give me clarification on the second part of my question concerning O-akylation?

 

[Rabolisk]

pKa of 19 is not considered an acidic site. Would you call water an acid?

 

[UIUCstudent]

pKa of 19 is not considered an acidic site. Would you call water an acid?

Oh good point!

 

[orgohacks]

The alpha hydorgen of a carbyonyl has a pKa of 19. On a passage would this be considered an acidic site?
Let's say a ethanoic acid as an example. Would this be considered a diprotic species?

Also, what does BR mean when it says "alkyl bromides and chlorides yield more O-akylation side products than akyl halides"? This is in relation to the carbanion doing a nucelophilic subsitution reaction on alkyl halid resulting in a longer ketone molecule. BR doesn't seem to expand on what O-akylation is.

O-alkylation refers to the alkyl halide attacking the oxygen of the enolate instead of the carbon, but the way the sentence is written it doesn't make sense to me (alkyl chlorides and bromides *are* alkyl halides, after all)