r8 dds

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Allylic carbocation or tertiary carbocation?

Edit: Given a primary alcohol, say ethanol and react with H2SO4, does H2SO4 give an ester or does it go through an elimination reaction?
I was debating, and I figured if given 2 moles of the reactant, then H2SO4/heat would give an ester. But with 1 mol of the reactant and just H2SO4/heat, it will go through elimination. Correct or no?
 
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Pat Kelly

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tert>allylic (pg. 377 McMurry)

Not sure if i understand your second question
 

bakanoisha

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Achiever says the opposite too... Allylic is more stable than tertiary carbocation...
It's b/c the allylic carbocation is resonance stabilized. Anytime you see resonance and carbocation, think (relatively) "stable".
 
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Oh yeah? What number?
I don't remember which number right now, but I am pretty sure one of the questions specifically covered this. I also saw somewhere online that allylic and benzylic carbocations are more stable than similar tertiary ones due to resonance.

Vinylic (if cation is actually on one of the two Carbons in double bond) is quite unstable on the other hand.
 
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really???? Destroyer says the opposite ........
It depends...you can't always think in terms of allylic, benzyllic, etc...

You've got think about it a little more sometimes.

Say in the example of a primary allylic carbocation that resonates between two primary allylic carbocations; such a carbocation is about equal in stability to that of a secondary carbocation and thus less stable than a tertiary.

However, a TERTIARY allylic is greater in stability than a tertiary carbocation because the carbocation is already tertiary AND there is delocalization that allows for even more stability than the simple tertiary carbocation.

A secondary allylic carbocation is about equal in stability to that of a tertiary carbocation.

It's not always cut and dry. Sometimes you have to examine the structures...
 

Maygyver

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I was taught allylic was more stable due to resonance too.
 

Pat Kelly

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It depends...you can't always think in terms of allylic, benzyllic, etc...

You've got think about it a little more sometimes.

Say in the example of a primary allylic carbocation that resonates between two primary allylic carbocations; such a carbocation is about equal in stability to that of a secondary carbocation and thus less stable than a tertiary.

However, a TERTIARY allylic is greater in stability than a tertiary carbocation because the carbocation is already tertiary AND there is delocalization that allows for even more stability than the simple tertiary carbocation.

A secondary allylic carbocation is about equal in stability to that of a tertiary carbocation.

It's not always cut and dry. Sometimes you have to examine the structures...
Took it right out of McMurry - either that or you memorized it cold - thanks for the notes
 
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r8 dds

r8 dds

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It depends...you can't always think in terms of allylic, benzyllic, etc...

You've got think about it a little more sometimes.

Say in the example of a primary allylic carbocation that resonates between two primary allylic carbocations; such a carbocation is about equal in stability to that of a secondary carbocation and thus less stable than a tertiary.

However, a TERTIARY allylic is greater in stability than a tertiary carbocation because the carbocation is already tertiary AND there is delocalization that allows for even more stability than the simple tertiary carbocation.

A secondary allylic carbocation is about equal in stability to that of a tertiary carbocation.

It's not always cut and dry. Sometimes you have to examine the structures...
Awesome thanks killer!