Comments on: Antiperiplanar Relationships: The E2 Reaction and Cyclohexane Rings

By: KD

KD — Sun, 23 Jun 2024 14:12:05 +0000

Hey!Got stuck in a point,you say that the Br needs to be axial in order to go through E2,but crap in the 4th question of your quiz the methyl cyclohexane without any axial Br does goes through E2.I understand that it works out because of being anti-periplanar,but please,I think it will be best to be less specific about the Br being axial in some parts of the Reply is highly appreciated.

By: AK

AK — Sun, 11 Jul 2021 14:40:23 +0000

For an axial CH3 and Br group in cyclohexane ring, the E2 is slower, and the reason you why is because “equilibrium position lies more to the other chair conformation (with LG and CH3 in equatorial), not the required chair (with LG and CH3 in axial)”, so by kinetics, rate is slower as concentration of required chair is lower.

But in other places, the reason said is because the “transition state for the chair having CH3 and Br in axial position is more unstable, so activation energy is larger”.

Which explanation is correct?

By: medicine french student

medicine french student — Wed, 11 Dec 2019 09:30:06 +0000

Wow that was very helpful thanks a lot!

By: James Ashenhurst

James Ashenhurst — Fri, 27 Sep 2019 02:39:39 +0000

In reply to Fish. Draw it out. It would still be 4-methyl cyclohexene, so it can't be a constitutional isomer. Does it look superimposable on the *other* 4-methyl cylohexene? : - )

By: Fish

Fish — Sun, 15 Sep 2019 03:00:34 +0000

Your explanation and pictures are very helpful, thank you. But with the elimination products, the other unshown product is not enantiomer but a constitutional isomer, isn’t it? I’m afraid if I understood something totally wrong. :(

By: James Ashenhurst

James Ashenhurst — Thu, 05 Sep 2019 18:36:12 +0000

In reply to Nata. Glad you find the website helpful Nata!

By: James Ashenhurst

James Ashenhurst — Thu, 29 Aug 2019 20:42:58 +0000

In reply to Shaurya. It's safe to assume the t-butyl group will prefer to be equatorial. With respect to the 1-bromo group, E2 will only occur when the Br is axial. So you'll have different rates of reaction for cis- and trans- 1-bromo-4-t-butylcyclohexane, since one will have an axial Br when t-butyl is equatorial, and the other will only have an axial Br when the t-butyl is axial. You can determine for yourself which elimination will be faster. The situation is further complicated with 1-bromo-2-methyl-4-t-butyl cyclohexane depending on the stereochemistry of the methyl group.

By: Shaurya

Shaurya — Sat, 14 Apr 2018 20:15:24 +0000

Can you explain dehydrohalogenation in 1-bromo-2-methyl-4-tertiarybutyl cyclohexane

By: Junkie

Junkie — Mon, 19 Mar 2018 05:15:44 +0000

In reply to james. Yes, that is a valid point.

By: Nata

Nata — Fri, 25 Nov 2016 06:55:36 +0000

Hi James,

Just want to thank you for such a wonderful website! I am a Biochemistry major, and Organic Chemistry has been my passion; however; there are times where some of the concepts get confusing, and your website helps to remind myself that everything in chemistry should make sense!

Thank you!