E1/e2

[au5233]

Hey Guys,

so I seem to be having some problems figuring out whether a reaction will undergo Sn1/Sn2/E1/E2...but primarily deciphering between E1/E2. I have been using Dr. Romano's Organic Odyssey and he keeps doing E2 reactions yet there is a protic solvent involved in the reaction. Shouldn't they be E1? As well, in the Kaplan online Elimination workshop, it says a more hindered substrate is favored by E2. But that makes NO SENSE to me because hinderance should favor E1 (more stable carbocation) and hinderance would make an E2 concerted attack difficult.

This is another problem I find confusing from kaplanL:

A central carbon with 3 ethyl groups attached to it, as well a bromine atom is being reacted with a hydroxide ion in menthanol.

I think "strong base, protic, thus E1"

They say "The base/nuceophile is OH-, a strong base and a strong nucleophile. However, the substrate is tertiary halide therefore we should not expect a substitution reaction...it is E2".

If OH- is a strong nucleophile as well and we have a tertiary, why are they claiming this would not be expected to undergo substitution??

If anyone can help me, you would truly be helping me out so much. Everything seems so contradictory with this stuff!

Thanks everyone.

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[jdoc04]

It sounds like you have the rxn conditions backwards. Search SN1 SN2 E1 E2 there is an excellent post somewhere that lays out all the conditions very clearly.

 

[Mstoothlady2012]

E1 prefers tertiary halide whereas E2 prefers primary. But if you have a strong base E2 is preferred eventhough the halide is tertiary. E1 takes place when there is protic solvent with a nonbasic nucleophile. You have to have both things in order to perform E1. Whenever you have a strong basic nucleophile always choose E2 as your first priority.

I hope this helps. Let me know if you need further clarification.

Hey Guys,

so I seem to be having some problems figuring out whether a reaction will undergo Sn1/Sn2/E1/E2...but primarily deciphering between E1/E2. I have been using Dr. Romano's Organic Odyssey and he keeps doing E2 reactions yet there is a protic solvent involved in the reaction. Shouldn't they be E1? As well, in the Kaplan online Elimination workshop, it says a more hindered substrate is favored by E2. But that makes NO SENSE to me because hinderance should favor E1 (more stable carbocation) and hinderance would make an E2 concerted attack difficult.

This is another problem I find confusing from kaplanL:

A central carbon with 3 ethyl groups attached to it, as well a bromine atom is being reacted with a hydroxide ion in menthanol.

I think "strong base, protic, thus E1"

They say "The base/nuceophile is OH-, a strong base and a strong nucleophile. However, the substrate is tertiary halide therefore we should not expect a substitution reaction...it is E2".

If OH- is a strong nucleophile as well and we have a tertiary, why are they claiming this would not be expected to undergo substitution??

If anyone can help me, you would truly be helping me out so much. Everything seems so contradictory with this stuff!

Thanks everyone.

 

[au5233]

Hey Thanks Guys, that did help. I also read some more up on it which cleared up some questions I had. I use to always look at the solvent right away, but obviously the solvent isn't the thing you should focus on...seeing the Kaplan example I mentioned did E2 in a protic solvent.

 

[azdds2008]

Just curious if anyone has a link to that SN1 SN2 E1 E2 post that expalins the conditions... thanks

 

[jdoc04]

Just curious if anyone has a link to that SN1 SN2 E1 E2 post that expalins the conditions... thanks

http://forums.studentdoctor.net/showthread.php?t=419097

Its 2 or 3 posts down. Props to the person who put it together. Much clearer than my ochem text which has the conditions scattered through several chapters.

Good Luck!!