Sn1,sn2,e1,e2?

[ranark]

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Hi, I am getting confused with these 4 reactions.. I can tell SN1 and SN2 apart but i cant tell E1 from SN1, E2 from SN2 or E1 from E2....can anyone break them down simply for me..Thanks alot.. i am stressing out right about now.

 

[sinned]

http://www.personal.psu.edu/faculty/t/h/the1/e2.htm

 

[ranark]

Thanks sinned.. its a good website.. i have a question though.. it says "Secondary alkyl halides give SN2 with good nucleophiles; strong bases promote E2 pathways ".. dont strong bases make good nucleophiles.. so arent these two requirements the same thing or am i just confused?

http://www.personal.psu.edu/faculty/t/h/the1/e2.htm

 

[ItsGavinC]

Thanks sinned.. its a good website.. i have a question though.. it says "Secondary alkyl halides give SN2 with good nucleophiles; strong bases promote E2 pathways ".. dont strong bases make good nucleophiles.. so arent these two requirements the same thing or am i just confused?

Indeed, strong bases make excellent nucleophiles. Remember though, that SN1 and E1 reactions often occur at the same time, and the same with SN2 and E2 reactions.

 

[luder98]

Thanks sinned.. its a good website.. i have a question though.. it says "Secondary alkyl halides give SN2 with good nucleophiles; strong bases promote E2 pathways ".. dont strong bases make good nucleophiles.. so arent these two requirements the same thing or am i just confused?

Strong bases love proton H, thus, they will attack the H to promote E2. Watch out for the steric compound too.

 

[ranark]

So then how do you differentiate between E2 and Sn2 besides using highly substituted groups for E2?

Strong bases love proton H, thus, they will attack the H to promote E2. Watch out for the steric compound too.

 

[sinned]

say you have OH- , if the substrate is usually tertiary, then it will go through E2 mostly and make a double bond...if it is a primary, then it will go through SN2 most likely, and if it's a secondary, it will go through both in an appreciable amount...but remember even if it is a tertiary, it will have "some" SN2 products, albeit a very small amount...

 

[luder98]

say you have OH- , if the substrate is usually tertiary, then it will go through E2 mostly and make a double bond...but remember even if it is a tertiary, it will have "some" SN2 products, albeit a very small amount...

i never heard about this before. my understand is that substrates with tertiary will not go x2. they will go x1 since stable carbion will form. on the other hand, primary substrates will not go x1.

 

[luder98]

So then how do you differentiate between E2 and Sn2 besides using highly substituted groups for E2?

i only know of two ways to control the two types of rxn. both are mentioned in kaplan's. bulky group and strong base will promote E2.

 

[DrTacoElf]

i only know of two ways to control the two types of rxn. both are mentioned in kaplan's. bulky group and strong base will promote E2.

I will also add that

High temp favors E1 and E2 over SN1 and SN2. Sterics hinder Substitution reactions much more so than elimination.

 

[phosphorylation]

http://www.personal.psu.edu/faculty/t/h/the1/e2.htm

many thanks...