lgnoring double-bond stereochemistry, what products would you expect from elimination reactions

Lgnoring double-bond stereochemistry, what products would...

Key Concepts

Elimination Reaction Mechanisms

Elimination reactions occur when a leaving group and a hydrogen atom are removed from adjacent carbon atoms, forming a double bond. These reactions can proceed via different mechanistic pathways, such as the concerted, one-step E2 mechanism or the stepwise, carbocation intermediate-driven E1 mechanism. The choice between these mechanisms depends on factors like the structure of the alkyl halide, the strength of the base, and the reaction conditions.

Zaitsev's Rule

Zaitsev's rule is a guiding principle in elimination reactions, stating that the major product is typically the more substituted alkene. The increased substitution around the double bond generally leads to greater stability due to hyperconjugation and inductive effects, making it the favored product when multiple elimination pathways are possible.

Regioselectivity in Elimination Reactions

Regioselectivity refers to the preference for forming one constitutional isomer over another when there are multiple possible sites for elimination. In elimination reactions, the positioning of the double bond (i.e., which hydrogen is abstracted) is influenced by factors such as steric hindrance, the nature of the leaving group, and the overall stability of the potential alkene products. This principle is key to predicting which product will be major in a given elimination reaction.

Transcript

00:01 So we have different halalcanes and we're asked, what would happen if we performed elimination reactions? so essentially, what products would we get? so when performing elimination reactions, it's important to remember that you're essentially deprotonating the hydrogen on the adjacent carbon of the alkaliad.

00:20 So an important thing to note there is that you're not deprotonating the hydrogen from the carbon that is connected to the alkyol halide.

00:27 You're doing it on the adjacent carbon.

00:29 So say for example we have molecule a and we're looking at the adjacent hydrogens.

00:37 So say for example, one of these hydrogens and we performed an elimination reaction in which we have a base deprotonating one of these hydrogens.

00:47 It doesn't matter which one because they're essentially the same.

00:52 And now these electrons which were connected to the hydrogen get pushed down towards this bond and now they're shared between these two carbons such that they're now sb2 hybridized.

01:03 So the product that you would get from that, it's going to look something like this, where you had the bromine as a leaving group here because it's a good leaving group, and now we get an alken that forms here.

01:22 However, there's also another product that can form because there's more adjacent hydrogens, or another one, rather.

01:31 So let's say we do that.

01:33 We draw the same thing.

01:38 For now we're looking at this hydrogen here.

01:45 So when we deprotonate it and perform the elimination, reaction, these electrons are going to go to these carbons here, or they're going to be shared between these carbons, and then we're going to have bromine as a leaving group, and we're going to generate the following alken product.

02:03 It's going to look something like this.

02:11 Now, the question also asks us to determine which one is the major product.

02:17 So recall zitesab's rule that the more substituted alken will be the more major product.

02:24 And from the top product here, we see that we are.

02:29 Are tri -substituted, or i'm sorry, we're die -substituted, since we only have two carbons connected to that.

02:40 Whereas in the second product here, we are tri -substuted because we have three connecting carbons here.

02:50 So we would say that the second product here is the major product.

02:58 Well, the first product we have saying would be our minor product.

03:10 Oh, i'm sorry, we're looking at the, not looking at this carbon here.

03:16 You're looking at this carbon, but still try -substituted.

03:19 And this would be the major product.

03:22 So we'll say, for example, we had another halalcane, and we do the same thing.

03:29 So let's say we choose this hydrogen first.

03:37 Let's go ahead and draw it in green here.

03:38 So we have this hydrogen first.

03:41 And we're performing another elimination reaction, so we depronate it.

03:57 And now these carbons get the electrons and this chlorine leaves.

04:03 So we get the following product.

04:15 And there's multiple products.

04:16 That we can form here...

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