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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: RH111 on April 25, 2021, 04:22:37 AM

Title: E1 vs E2 Reaction Products
Post by: RH111 on April 25, 2021, 04:22:37 AM

Hi,

I was wondering what differs between the products of E1 and E2 reactions.
I understand they are different mechanisms, with E1 occurring in 2 steps and E2 in 1 step, but I am confused as to what the actual difference between the products of both reactions are.
Do they both produce two structural isomers?

Thanks!
RH111

Title: Re: E1 vs E2 Reaction Products
Post by: Orcio_87 on April 25, 2021, 05:18:28 AM

E2 requires anti-periplanar geometry - H and X (leaving group) must lie opposite each other, so in some cases it gives only one product.

https://en.wikipedia.org/wiki/Zaitsev%27s_rule#Stereochemistry

Title: Re: E1 vs E2 Reaction Products
Post by: RH111 on April 27, 2021, 03:58:31 AM

Thanks! Is it possible in some cases for both the E-1 and E-2 mechanisms to give the same products (structurally) if both adjacent carbons to the leaving group have hydrogens that have anti-periplanar geometry with the leaving group?

~RH111

Title: Re: E1 vs E2 Reaction Products
Post by: kriggy on April 27, 2021, 06:10:18 AM

Quote from: RH111 on April 27, 2021, 03:58:31 AM

Thanks! Is it possible in some cases for both the E-1 and E-2 mechanisms to give the same products (structurally) if both adjacent carbons to the leaving group have hydrogens that have anti-periplanar geometry with the leaving group?

~RH111

Hardly in my opinion because E2 requires formation of carbocation which is not stable on substrates that undergo E1.

Title: Re: E1 vs E2 Reaction Products
Post by: Orcio_87 on April 27, 2021, 09:59:22 AM

@kriggy

Quote

Hardly in my opinion because E2 requires formation of carbocation which is not stable on substrates that undergo E1.

E1 requires formation of carbocation, E2 requires only sufficient concentration of the base.

@RH111

Quote

Is it possible in some cases for both the E-1 and E-2 mechanisms to give the same products (structurally) if both adjacent carbons to the leaving group have hydrogens that have anti-periplanar geometry with the leaving group?

If there are two hydrogens on every adjacent carbon atoms, then yes - E2 can give same mixture of products as E1.

Title: Re: E1 vs E2 Reaction Products
Post by: Meter on April 27, 2021, 11:01:22 AM

Quote from: Orcio_Dojek on April 27, 2021, 09:59:22 AM

@kriggy

Quote

Hardly in my opinion because E2 requires formation of carbocation which is not stable on substrates that undergo E1.

E1 requires formation of carbocation, E2 requires only sufficient concentration of the base.

I'm sure pKb is also a factor. I don't think E2 occurs in water (to any significant degree) and that has "100%" concentration.