CHEM 2100 Addition Reaction Mechanisms

Hydrohalogenation

Addition of HX with H on less substituted side (Markovnikov)

If reacted with HBR what reaction would occur?

Hydrohalogenation with H on less substituted carbon

If reacted with HBR/ ROORwhat reaction would occur?

Hydrohalogenation but anti markovnikov (H on more substituted position)

Catalytic Hydrogenation

Addition of H in the presence of a metal catalyst, watch out for meso compounds

If reacted with H2/Pt what reaction would occur?

Catalytic hydrogenation

Dihydroxylation

Adding OH across an alkene

If reacted with 1)ROC3H/ 2)H3O+ what reaction would occur?

Anti dihydroxylation

If reacted with mcPBA or peroxyacteic acid (CH3O3H)/H/H20 what reaction would occur?

Anti dihydroxylation

If reacted with Na2SO3/ H2O reaction would occur?

Syn dihydroxylation

If reacted with NaHSO3/H2O what reaction would occur?

Syn dihydroxylation

If reacted with 1)OsO4/ 2) NAHSO3,H2O what reaction would occur?

Syn dihydroxylation

If reacted with KMnO4, NaOH/ cold what reaction would occur?

Syn dihydroxylation

Acid Catalyzed Hydration

Addition of OH on the more substituted carbon (Markovnikov)

If reacted with H3O+ what reaction would occur?

Acid catalyzed hydration

If reacted with H2SO4 what reaction would occur?

Acid catalyzed hydration

Hydroboration Oxidaiton

Installs OH at the less substituted carbon (anti- Markovnikov)

If reacted with 1)BH2, THR/ 2) H2O2, NaOH what reaction would occur?

Hydroboration Oxidation

Halogenation

Addition of either CL2 or Br2 across an alkene, with anti addition

If reacted with Br2 what reaction would occur?

Halogenation

Halohydrin formation

OH added at more substituted position

If reacted with Br2/H2O what reaction would occur?

Halohydrin formation

Ozonolysis

Cleaving of the double bond into separate molecules

If reacted with 1) O3/ 2)DMS what reaction would occur?

Ozonolysis

If reacted with 1)O3/ 2)Zn/H2O what reaction would occur?

Ozonolysis

Hydrohalogenation mechanism

1. Alkene acts as a base and accepts a proton

2. Carbocation formation (with possible rearrangements)

3. Nucleophilic attack

• lookout for enantiomers!

Acid Catalyzed Hydration Mechanism

1. Proton transfer (alkene is protonated) resulting in a carbocation forming

2. Nucleophilic attack: Water acts as a nucleophile attacking the carbocation intermediate

3. Proton transfer: water functions as a base deprotonating the oxonium ion

Hydroboration oxidation mechanism

1. Hydroboration, the alkene attacks the B simultaneously as the H attacks the C, first step re[easts for each B-H bond forming a trialkylborane

2. Oxidation:

1. Proton transfer: OH- ions functions as a base and deprotonates hydrogen periodic forming a hydroperoxide

2. Nucleophilic attack: hydroperpxide acts as a nucleophile attacking the trialkylborane

3. Rearrangement (alkyl group migrates explaining a hydroxide ion *happens again until trialylborane turns into trialkoxyborane

3. Nucleophilic attack: hydroxide ion attacks trialkoxyborane

4. Loss of a leading group, all oxide is expelled removing negative change form boron

5. Proton transfer

Halogenation Mechanism

1. Nucleophilic attack & loss of a leaving group (simultaneously)

Alkene functions as nucleophile and attack Bromine, expelling bromide as a LG which forms a bridged intermediate (bromonium ion)

2. Bromide acts as a nucleophile in an SN2 process (backside attack) attacked the Br ion (why the product is anti addition)

Halohydrin formation mechanism

1. Nucleophilic attack & loss of LG (simultaneously), expels Br

• can be drawn as a transition state

1. Nucleophilic attack: water functions as nucleophile attacking the Br ion in an SN2 process

2. Proton transfer: water serves as a base and deprotonates the oxonium ion resulting in anti addition

Dihydroxylation mechanism

1. Formation of an epoxide (transition state)

2. Acid catalyzed opening of an epoxide

• proton transfer (epoxide gets protonated)

• Nucleophilic attack water acts as a nucleophile and in an SN2 process attacks. The protonated epoxide

• Proton transfer : water acts ad a base deprotonation the oxonium ion