Give the major product(s) obtained from the reaction of each of the following with HBr:

Name: Problem 14, Chapter 4: Organic Chemistry
Uploaded: 2021-04-22T22:27:50-08:00
Duration: 4 min 37 s
Channel: Temi Ajayi
Description: Give the major product(s) obtained from the reaction of each of the following with HBr:

step 1 Okay, so here we're looking at some HB or halogenation questions. So first starting off with 3 m

Give the major product(s) obtained from the reaction of each...

Key Concepts

Electrophilic Addition Mechanism

The electrophilic addition mechanism describes how reagents like HBr react with alkenes. The process begins with the alkene acting as a nucleophile and attacking the electrophilic proton (H+) from HBr, forming a carbocation intermediate. Subsequently, the bromide ion, acting as a nucleophile, attacks the positively charged carbon, leading to the formation of the bromoalkane product. This mechanism highlights the step-wise nature of the reaction and the role of intermediate stability in determining product distribution.

Free Radical Addition (Anti-Markovnikov Reaction)

Under conditions where peroxides are present, the addition of HBr to alkenes can proceed via a free radical mechanism, resulting in anti-Markovnikov product formation. In this pathway, radicals are generated and the bromine radical adds to the less substituted carbon atom first, reversing the regiochemical outcome predicted by Markovnikov's rule. This concept is important when considering alternative mechanisms that lead to different product distributions in halogenation reactions.

Markovnikov's Rule

Markovnikov's rule is a guiding principle in the electrophilic addition of hydrogen halides to unsymmetrical alkenes. It states that in the addition of HX (where X is a halogen) to an alkene, the hydrogen atom will attach to the carbon having more hydrogen substituents, while the halide attaches to the carbon with fewer hydrogen atoms. This rule is based on the stability of the carbocation intermediate formed during the reaction, as more substituted carbocations are more stable.

Carbocation Intermediate Formation and Rearrangement

During the electrophilic addition of HBr to an alkene, the reaction typically proceeds through the formation of a carbocation intermediate after the protonation of the double bond. The stability of this intermediate is crucial, as it may undergo rearrangements (such as hydride or alkyl shifts) to form a more stable carbocation before the bromide ion attacks. Understanding this concept is key to predicting the major product of the reaction.

Transcript

00:01 Okay, so here we're looking at some hb or halogenation questions.

00:05 So first starting off with 3 methyl butene.

00:11 Okay, well basically form here's the mark product.

00:18 So considering we will look at the secondary carbocon versus hydrogen extraction being taken place on the primary site, basically form the three.

00:36 Bromination there to form this compound and that's basically the basic mechanism for all the other ones it's not if you look at a methyl cyclooxane cap so what we basically form here with an hbr is that tertiary carbokadion and then we get some nice bromination at that site.

01:18 The next one we have here is 4 methylpentine, 4 like that, and again we will form a carbonyon on the secondary site as opposed to the primary to then also get the 4 bromol halite.

01:44 Okay.

01:47 The next compound was similar to this one over here.

01:53 So here we have a cyclohexene.

01:55 And that looks like that.

01:57 Looking like that.

02:01 So what's going to happen here is the exact same.

02:05 There's the tertiary versus secondary.

02:07 So of course, considering hbr works through markovnikov mechanism, we will get bramination at the tertiary site right there.

02:17 Okay, so now we have another compound here that looks like this...