Predict the elimination products of the following reactions, and label the major products. (a) c

Predict the elimination products of the following reactions,...

Key Concepts

Zaitsev’s Rule

This rule states that the more substituted alkene, which is typically thermodynamically more stable, is favored as the major product in elimination reactions. In E2 processes, when there is a choice between forming different alkenes, the pathway leading to the more substituted, stable alkene is preferred, guiding which elimination product will predominate.

Stereochemistry in Cyclohexane Systems

Cyclohexane derivatives display stereochemical effects that arise from chair conformations. The disposition of substituents (axial vs equatorial) in cis- and trans-isomers influences the possibility of achieving the anti-periplanar orientation necessary for E2 elimination. Conformational analysis is key in predicting which hydrogen-leaving group pairs are antiperiplanar and thus determine the major product.

E2 Elimination Reaction

This is a concerted mechanism in which a base abstracts a proton from a ?-carbon while the leaving group departs simultaneously, leading to the formation of a double bond. The mechanism does not involve discrete carbocation intermediates, and reaction conditions favoring strong bases in polar protic solvents often promote E2 eliminations.

Anti-periplanar Geometry

For an efficient E2 elimination, the hydrogen that is being abstracted and the leaving group must be aligned in an anti-periplanar arrangement. This spatial orientation allows optimal overlap of orbitals during the elimination step, a requirement that becomes particularly significant in cyclic systems where conformational constraints may limit the availability of such arrangements.

Transcript

00:01 Okay, so i want to give the elimination products for the following reactions.

00:03 The first one is r2 bramaxine.

00:05 We're acting with a high concentration of hydroxide.

00:13 So we're going to put the bramine on the wedge.

00:17 This group is 1 is the highest atomic number.

00:19 This is 2.

00:20 It's a high atomic weight than the methyl group.

00:22 That's 3.

00:23 The hydrogen is 4 is the lowest atomic number.

00:26 1 to 2, 2 to 3.

00:28 3 to 1, ignoring 4 is clockwise, which is r.

00:32 And so you're acting with a high concentration of hydroxide.

00:35 In solution, this be sodium and the hydroxide ion.

00:41 And this is a strong base.

00:43 So we don't really need the formation of the carbicata intermediate.

00:45 We can just attack the aquilite directly.

00:48 But in the case of e2, it's going to behave more as a base than a nucleophile, and grab a proton from the adjacent carbon leading to the stable alken.

00:58 It's going to grab a proton from this carbon to give us a more stable, more substituted alken.

01:04 And as a result, this group is going to leave.

01:09 And we'll get 2 hexene.

01:12 If we compare this to reacting with water, water is a weak base and a weak nuclear file, so we really need the formation of that carbon cadet intermediate, and this is going to favor actually e1 instead.

01:28 It would compete with s &1.

01:30 We can increase the possibility of e1 by adding heat to this reaction, this would favor sn2.

01:38 So if you have a weak base and a weak nuclear file, it's going to favor sn1 and e1, and the opposite would favor sn2 and e2.

01:46 But it's going to lead to the same product, just different mechanism.

01:53 And we would also get h3a plus as a side product.

01:58 And then for c, we have trans 1 chloro, 2 methyl cyclohexene.

02:05 So just putting one group in the front and one in the back.

02:13 And we're first going to react this with a high concentration of methoxide.

02:24 So the conjugate acid of methoxide is methanol, which is weak, and therefore it's going to be a strong base.

02:34 And it's also going to favor the e2 reaction.

02:39 It's occurring in one step.

02:42 And with these reactions, it has to grab a proton from the adjacent carbon, which is anti -to -the -leaving group.

02:50 So it can grab, so the carbon adjacent to the leaving group is this one and this one, but only this one has a hydrogen that's anti -tileving group...

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