E1/e2

[osimsDDS]

I am having a very difficult time distinguishing between E1 and E2 reactions and what they do...does any one have definitive answer to these and could explain the difference to me would be very helpful...thank you

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[PooyaH]

I am having a very difficult time distinguishing between E1 and E2 reactions and what they do...does any one have definitive answer to these and could explain the difference to me would be very helpful...thank you

The only way I distinguish it from E1 is when a strong base is being used! Also whenever you see a primary Carbon, it must be E2 or SN2!

 

[pistolpete007]

they ay i thought and correct me if im wrong

E1 and SN1 is usually together except if u have a lot of heat then its E1

E2-is with STRONG BASE such as KOH....and if u have tertiary base then its also E2 but least substituted...

 

[Maygyver]

I am having a very difficult time distinguishing between E1 and E2 reactions and what they do...does any one have definitive answer to these and could explain the difference to me would be very helpful...thank you

E1
-Two steps: 1. Carbon-Halide bond breaks
2. Hydrogen is eliminated
-Occurs with tertiary alkyl halides and sometimes secondary alkyl halides. Because these are bulky, they favor the smaller bases rather than bulky bases like E2 which have trouble accessing the protons.
-Usually weak nucleophile. HOMe, H2O, H3CSH for example.
-Competes with SN1 due to having a common intermediate (carbocation) adding heat will favor E1 over SN1
-Can have carbocation rearangements
-Regioselective. Follow Zaitsev's rule and will form the more stable alkene.

E2
-One Step: Base removes proton, proton donates electrons to form double bond and kicks off halide.
-Occurs with primary alkyl halides and sometimes secondary alkyl halides. This is because the strong bulky base cannot remove protons from a bulky alkyl halide. These primary and secondary alkyl halides have readily accessible protons.
-Polar aprotic solvent
- Beta hydrogen and alpha halide must have an antiperiplanar relationship (180 degrees)

Here is a chart for you. I will try my best to reprint it (from my college notes). If you have an questions ask.
Tertiary Alkyl Halides + strong nuc = E2
Tertiary Alkyl Halides + strong/bulky nuc = E2
Tertiary Alkyl Halides + weak nuc = SN1 +E1

Secondary Alkyl Halides + strong nuc = E2 + SN2
Secondary Alkyl Halides + strong/bulky nuc = E2
Secondary Alkyl Halides + weak nuc = E1 + SN1

Primary Alkyl Halides + strong nuc = SN2 + E2
Primary Alkyl Halides + strong/bulky nuc = SN2 + E2
Primary Alkyl Halides + weak nuc = NO RXN

Strong nuc = NaOMe
Strong/bulky nuc = NaO(CH3)3
Weak nuc = HOMe

I hope this helps

 

[DCRedskinsRule]

Osims...I think I have a pretty decent understanding of it and experience with the Kaplan stuff so if those explanations still were not enough, PM me and I'll do my best as well.

 

[DRHOYA]

To simply answer E1 vs E2. E1 is a two step mechanism with a carbocation intermediate, where tertiary is more stable. E2 is a one step mechanism with primary/secondary. Another distinguishing feature of E2 is a big strong bulky base. Hope that helps.

 

[DCRedskinsRule]

Longest. PM. Ever.

Sorry.

 

[PreDent2009]

E1 and SN1 are in competition with eachother always, just as E2 and SN2 are competing reactions. The easiest way to distinguish between E1 and E2 is that E1 only occurs with a strong acid (concentrated with heat) such as sulfuric or phosphoric reacting with an alcohol. Any other acid such as HBR, HCL, etc reacting with an alcohol with always give SN1. I could give you a detailed reason for why this occurs but this is the short, easy way to know when an E1 reaction occurs. PM me if you want the explanation. Otherwise, just know that E2 is a strong base/strong nucleophile with a leaving group. SN2 is a strong base/strong nucleophile reacting with a primary or secondary halide that does not have shrubbery nextdoor. With a secondary leaving group, you usually get a mixture of E2 and SN2 so your reaction conditions have to favor one or the other. Mixtures are pointless in Organic Chem so you always favor one reaction over the other.

I am having a very difficult time distinguishing between E1 and E2 reactions and what they do...does any one have definitive answer to these and could explain the difference to me would be very helpful...thank you