2011 Destroyer OC #31 (page 15)

[qkchen]

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hi guys,

i am looking at Destroyer OC #31 on page 15 of 2011 version. i figured out the reaction but was wondering why the outermost methyl protons were more acidic compared to the alpha-protons that is more internal. thanks for any help!

 

[wizi]

hi guys,

i am looking at Destroyer OC #31 on page 15 of 2011 version. i figured out the reaction but was wondering why the outermost methyl protons were more acidic compared to the alpha-protons that is more internal. thanks for any help!

So basically, we have 2 alpha protons a and c.

According to Bronsted, Acid is the one donates its H+ (definition of acid).

--> which proton is more likely to be removed: a or c?

a, because its the outermost proton. Therefore its a better acid.



I hope that makes sense.

This is my explanation. Someone else might have a better explanation.

 

[wall1two]

So basically, we have 2 alpha protons a and c.

According to Bronsted, Acid is the one donates its H+ (definition of acid).

--> which proton is more likely to be removed: a or c?

a, because its the outermost proton. Therefore its a better acid.



I hope that makes sense.

This is my explanation. Someone else might have a better explanation.

wizi is 100% correct, but just to supplement (helps me memorize this crap) the alpha hydrogen that is outermost is more acidic because it can react with any given base more easily! it is the most vulnerable to base attack. kind of like the definition of a nucleophile being related to how easily is can form a bond with an electrophile, both definitions play off each-other in order to make this studying process as difficult as possible.

its not a great example for our reasons but you can see the base is removing the beta proton that is more acessable

 

[qkchen]

thank you guys, i guess it has to do more with accessibility so that is how i will come to understand it

 

[yappy]

This is interesting... does anyone know the name of this principal? In all my studies I have never heard this concept explained in this way... The terminal alpha H was selected due to steric hinderence making the internal alpha H unfavorable?

 

[invictusx]

This is interesting... does anyone know the name of this principal? In all my studies I have never heard this concept explained in this way... The terminal alpha H was selected due to steric hinderence making the internal alpha H unfavorable?

Well, it depends on the molecule. If it's a carbonyl, you might want to choose the alpha hydrogens, especially if it's a condensed carbonyl. If you want to eliminate, you have to consider steric. That's why you can't really do a SN2 on a tertiary carbon and thus proceed to E2. However, E1 and SN1 reactions are freely competitive because both share the same carbocation.

However, I would like to see the question because not all of us have the 2011 destroyer. Provide us with the question and answers so we can think about it and give you a better understanding of the question 😀