Alkene Additions and Oxidations

These flashcards cover key concepts regarding alkene additions and oxidations, focusing on reaction types, stereochemistry, and regiochemistry.

What is the outcome when two enantiomers react with an achiral reagent?

They react at the same rate because the rate determining step involves enantiomers of each other, resulting in no rate difference.

What results from the reaction of two enantiomers with a chiral reagent?

They may react at different rates due to forming diastereomeric transition states.

What type of products can be produced from achiral or racemic mixtures?

Only achiral or racemic products can be produced; if starting with optically inactive compounds, the results will also be optically inactive.

What is the stereochemistry outcome of syn vs anti addition?

Syn addition leads to a cis product, while anti addition leads to a trans product.

What is the regiochemistry of reactions involving alkene additions?

The regiochemistry is typically Markovnikov.

What must be true about KMnO4 for it to be effective in a reaction?

KMnO4 must be dilute and cold to ensure proper stereochemistry.

In the context of alkylation reactions, how does water influence the carbocation?

A water molecule is added to the carbocation and is followed by deprotonation, leading to both syn and anti products.

Describe the stereochemistry and regiochemistry when B is replaced by OH in an alkene reaction.

Stereochemistry is syn and regioselectivity is Anti-Markovnikov.

What is the stereochemistry for an addition of HX

Syn or anti addition

What is the regiochemistry of an addition of HX

Markovnikov, meaning it will add on the less substituted carbocation

Describe the process of the Addition of HX reaction

First, we will use the double bond (as a nucleophile) to attack H, which adds it to the less substituted carbon atom. This produces a carbocation on the more substituted carbon, where we will then use the nucleophile’s X electron pair to attack and add to the more substituted carbon.

What are the common halides used in addition of HX

Br, Cl, I

If the addition of HX occurs on a secondary carbocation, what can happen?

It can rearrange to a tertiary carbocation

What is the stereochemistry of Bromination/Chlorination?

anti

What is the regiochemistry of Bromination/Chlorination

There is no regiochemistry

Name the intermediate for this reaction

Cyclic bromonium ion which allows anti addition

Describe the reaction mechanism for bromination/chlorination

First we utilize the double bond on the carbon to attack one of the halogens, which will be added to one of the carbons. However, because Bromine is big and puffy, it ends up turning into a cyclic bromonium ion, added to both carbons. The second halogen then attacks from the bottom, breaking the cyclic ion and adding it to the other side. Both Brs are anti to each other now.

What is the stereochemistry for the halohydrin reaction

Anti

What is the regiochemistry of halohydrin reactions

Markovnikov

What reaction is halohydrin similar to?

Bromination/Chlorination, yet second addition is O nucleophile, either from water or an alcohol

Which carbon will O add to in the halohydrin?

The more substituted carbon

Describe the reaction mechanism for a halohydrin

His reaction contains OH and a halide. It has the same first step as bromination/chlorination, where we use the double bond to attack the Br, but because Br is so big, it becomes a cyclic bromonium ion. However, if we have a high concentration of water, we would use this to attack the more substituted carbon, breaking the cyclic ion and adding to the anti side. But now, the water has a positive charge due to its three bonds, so we deprotenate one of the hydrogens using more water, which will leave an end product of Br and OH on adjacent carbons.

What is the stereochemistry of H20 addition as Oxymercuration

syn or anti

What is the regiochemistry of addition of H20 as oxymercuration?

Markovnikov

What is the intermediate for addition of H20 as Oxymercuration?

3 membered mercurinium ion

How is OH added to the addition of H20 as Oxymercuration reaction

OH is added anti to Hg, but Hg is replaced by H. So, this can be syn or anti addition.

Can you use alcohol instead of water for addition of H20 as oxymercuration?

Yes, it results in an ether

Name the mechanism for addition of H20 as an acid catalyst

This is a rather known one, where we protonate the alkene(using the double bond) to create a carbocation. With this, we then add water to the carbocation. To get rid of the negative charge, we then deprotenate the water with another water, leaving an OH behind

What is the stereochemistry of addition of H20 acid catalyzed

syn and anti

What is the regiochemistry of addition H20 acid catalyzed

Markovnikov

Describe the mechanism for hydroboration/oxidation

Using a double bond, we use it to attack the H connected to BH3 molecule. This adds to the more substituted carbon, creating a carbocation on the less substituted ion, where we then attack with BH2. This is a syn addition. But then, we bring in HO2, where it will attack the boron to bind to it. But then, due to this, BH2 disconnects from the carbon and attaches to the O, which disconnects from the OH. From this, that OH will attack the BH2, removing it from the O and going off into the void. From this, we protenate the negative charge on the O to create OH

What is the stereochemistry of hydroboration/oxidation

syn

What is the regiochemistry of hydroboration/oxidation

Anti-Markovnikov

Describe the mechanism of hydrogenations

The hydrogen is added to the double bond via a diatomic hydrogen. It “slaps the ground” to pick up Hs, which are added to the syn side. This is usually in the presence of a metal catalyst: PdC, Pt, N.

What is the stereochemistry of Hydrogenation

syn

What is the regiochemistry of hydrogenation

There is none

Describe the mechanism of epoxidation

A alkene is reacted with meth-chloroperbenzoic acid. The double bond reaches out to attack the alcohol part of the ring. But this is a single step, forming a cyclic epoxide due to its tendancy to take make two bonds.

What is the stereochemistry of expoidation

syn

What is the regiochemistry of epoxidation

there is none

Describe the mechanism for epoxidation/ring opening

This is the method of opening an epoxide. It requires the mCPBA from before to make said epoxide, but then it is broken by hydronium ion donating an H to bind to the oxygen. Since it is then a positive charge on the oxygen, we attack the carbon with water to form a diol. This breaks the exposide ring, but there is another positive charge on this oxygen, so we deprotenate this again, resulting in anti-diol.

What other reaction is epoxidation ring opening analogous to?

Bromination

WHat is there stereochemistry of epoxidation ring opening

anti

What is the regiochemistry of epoxidation ring opening

there is none

Describe the mechanism for cyclopropanation

Cyclopropanation involves the attack of a carbene on a double bond. In doing so, this creates a three member propane ring on top of the alkene, connected to the other carbons.

What is the method of creating a dichlorocyclopropane?

A HCCl3 molecule reacts with OH, where the OH will deprotonate an H, creating CCl3-. But, one of the chlorines also leads, resulting in a dichlorocarbene. This attacks the double bond of an alkene, reacting with it to make a dichlorocyclopropane.

What is the simmons smith method of creating a cyclopropane

Utilizing CH2I2/Cu(Zn), the CH2I2 attacks a carbon double bond. This creates a propane like structure, but the Cu(ZN) removes the I to create a carbonoid. This results in a cyclopropane and an enantiomer.

What is the stereochemistry of cyclopropanation

syn

What is the regiochemistry of cyclopropanation

None

Describe the mechanism for dihydroxylation

Dihydroxylation is when an OsO4(or Osmium tetroxide) attacks an alkene. This attacks two of the Oxygen’s electron pairs, leading to the O to be bonded to each carbon as well as the rest of the osmium tetroxde. Then, you add water, which creates an unknown mechanism to generate two oxygens.

What is the final addition of dihydroxylation called?

1,2 diol

What is stereochemistry of dihydroxylation

syn addition

What is the second version of dihydroxylation? What is the exception

KMnO4, but MUST BE DILUTE AND COLD

Describe the mechanism for dilute and cold KMnO4

There is an unknown mechanism, but results in a 1,2 diol as well.

What is the stereochemistry of dihydroxylation?

syn

What is the regiochemistry of dihydroxylation?

None

Describe the mechanism of warm and concentrated KMnO4

Concentrated,warm KMnO4 results in an osidative cleavage of an alkene, leading to two ketones.

What is oxidative cleavage of KMnO4

chain shortening

If both groups of the alkene C are carbons in oxidative cleavage, what will you end up with?

Ketones

If there is one H on an alkene carbon in oxidative cleavage, what will you end up with?

carboxylic acids

If there are 2H on carbon alkenes in oxidative cleavage, what will you end up with?****

aldehydes, which can be reduces to a carboxylic acid, and then carbon dioxide

What is ozonologist?

Similar to KMnO4, this involves a cyclohexane double bonded to a another alkane group. This is reacted with ozone(O3), and then Zn/H3O+. THis cleaves it also into two carbonyl compounds. It is milder than KMnO4, easily controlled, and can isolate aldehydes.

What is the regiochemistry of oxidative cleavage?

None

What is the stereochemistry of oxidative cleavage

None