227 destroyer ochem 2010

[recyrb]

so this is a dieckman condensation, where the strong base deprotanates an alpha carbon. the long chain then attacks its self forming a ring.

so my question is, how do you know which alpha carbon to deprotonate?

2 of the answer choices differ, soley on which alpha carbon is deprotonated, which is bs, but how do you know which one??


2010 227 destroyer organic..

thanks

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[bharat008]

so this is a dieckman condensation, where the strong base deprotanates an alpha carbon. the long chain then attacks its self forming a ring.

so my question is, how do you know which alpha carbon to deprotonate?

2 of the answer choices differ, soley on which alpha carbon is deprotonated, which is bs, but how do you know which one??


2010 227 destroyer organic..

thanks

It doesn't matter which alpha-hydrogen you remove. In the end you are still attacking one of the carbonyl carbons (electrophile). Try to remove each of the alpha-H and draw out your products = in the end you will get the same answer. If you don't then you are probably doing something wrong..

 

[recyrb]

It doesn't matter which alpha-hydrogen you remove. In the end you are still attacking one of the carbonyl carbons (electrophile). Try to remove each of the alpha-H and draw out your products = in the end you will get the same answer. If you don't then you are probably doing something wrong..

bump and

just to clarify, but i am probably mistaking


the carbon chain is not symetrical to the carbonyls. so if you protonate one alpha carbon, then you the a 1/3 substituent, but protonating the other alpha carbon gives you 1/2--

this is where my confusion is because both of those are answer choices

thanks

 

[RING12]

bump and

just to clarify, but i am probably mistaking


the carbon chain is not symetrical to the carbonyls. so if you protonate one alpha carbon, then you the a 1/3 substituent, but protonating the other alpha carbon gives you 1/2--

this is where my confusion is because both of those are answer choices

thanks

you always need to attack the most acidic H. which is the one next to carbonyl group.

 

[bharat008]

bump and

just to clarify, but i am probably mistaking


the carbon chain is not symetrical to the carbonyls. so if you protonate one alpha carbon, then you the a 1/3 substituent, but protonating the other alpha carbon gives you 1/2--

this is where my confusion is because both of those are answer choices

thanks

Think of it this way. The alpha hydrogen on right only has 1 R group and the alpha hydrogen on left has 2 R groups. The more R groups you have the more they will donate the electrons and make the enolate less stable. Since the base (enolate is less stable), the acid is weak (in this case the alpha hydrogen won't be that acidic as compared to the alpha hydrogen with only 1 R group)..

Simple concept; the stronger the acid the weaker it's conjugate base (stable). In this case, we have 2 R groups which would make it less stable (reactive); therefore, the alpha hydrogen would be less acidic.

Think of it in terms of Ketone and Aldehyde. How Aldehyde's alpha hydrogen is more acidic than ketone's alpha hydrogen due to aldehyde having no R groups while ketone has 1 R group..

Hope that helps..