What stereoisomers would be formed from the reaction of each...

What stereoisomers would be formed from the reaction of each of the following alkenes with $\mathrm{OsO}_{4}$ followed by $\mathrm{H}_{2} \mathrm{O}_{2} ?$
a. trans-2-butene
b. cis - 2 -butene
c. cis - 2 -pentene
d. trans-2-pentene

Key Concepts

Formation of Enantiomers and Meso Compounds

The products of syn dihydroxylation can be either enantiomers or meso compounds depending on the starting alkene’s geometry. When a cis-alkene undergoes syn addition, the resulting diol typically forms a pair of enantiomers, while a trans-alkene yields a meso compound due to the presence of an internal plane of symmetry, rendering the molecule achiral.

Geometric Isomerism in Alkenes

Geometric isomerism refers to the cis and trans configurations possible around a double bond due to restricted rotation. The relative positions of substituents (either on the same side in cis isomers or opposite sides in trans isomers) play a crucial role in determining the stereochemical outcome when these compounds undergo syn addition reactions.

Syn Dihydroxylation

Syn dihydroxylation is a reaction mechanism where two hydroxyl groups are added to the same face of a carbon-carbon double bond. In this transformation, the addition occurs in a concerted manner, typically via the formation of a cyclic intermediate, such that both new substituents end up on the same side of the molecule.

Stereospecificity

Stereospecific reactions are those in which the stereochemical configuration of the reactants directly determines the stereochemistry of the products. In the context of syn dihydroxylation, the original geometry of the alkene (whether cis or trans) controls the relationship between the newly added -OH groups, leading to either enantiomeric or meso products.

Transcript

00:01 Okay, so we're going to get the products for the following reactions with osmoneum tetraoxide and peroxide.

00:05 First one is trans 2 -butene.

00:19 So this is going to add the alcohols in sin edition, and it will create a dial, which is two alcohols in the same structure.

00:26 In the case of trans, it can really attack either carbon because they're both equally as hindered.

00:33 So we're going to get the same products in the trans configuration, either both in the front or both in the back.

00:46 So you could also draw the anathema.

00:48 This side would be 1.

00:49 This is 2, 3, the hydrogen in the back is 4.

00:53 So this would be the s configuration.

00:55 And we could just draw r by putting the alcohols in the back, both in the back.

01:05 And for b, we have cystocene.

01:09 And with cis, this is where it matters, which side it attacks from.

01:14 Because we have these bulky methyl groups blocking front side attack.

01:18 These two are in the front.

01:19 So osmonium tetraoxide is going to, well, the opposite.

01:23 The oxygen of osmoneum tetraoxide is going to attack from the back while the oaken, the double bond of the alken is going to attack osmoneum.

01:42 So if these are on the front, it's going to have the alcohols of the back.

01:46 Therefore, it's going to be the structure.

01:50 If we just draw all butane as it is, we're going to get this...

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