Reactions of Alkenes: Mechanisms and Conditions

Hydrogenation

-Common Solvents: H₂/Pd

-Mechanism: Break π bond, add H to each C.

-Syn addition

Hydrohalogenation

- Common Solvents: H-X (X = Br, Cl)/ROOR

-Mechanism: Break π bond, add H to less substituted C.

-Shifts possible!

-Markovnikov (Anti with ROOR)

-Carbocation intermediate.

-Racemic product.

Halogenation

-Common Solvents: Br₂/CH₂Cl₂ (or similar)

-Mechanism: Break π bond, add Br/Cl to each C.

-Anti addition

-Bridged intermediate forms.

Think "Anti-addition Halogens."

Halohydrin Formation

-Common Solvents: Br₂/H₂O (polar protic solvent)

-Mechanism: Break π bond, add solvent to more substituted C and halogen to less substituted C. Remove H from added solvent.

-Markovnikov

-Anti addition

-Bridged intermediate forms.

Acid-Catalyzed Hydration

-Common Solvents: H₂O/H₂SO₄

-Mechanism: Break π bond, add H to less substituted C and OH to more substituted C.

-Markovnikov

-Racemic product.

-Carbocation intermediate

-shifts possible!

think 'AM': "Acid, Markovnikov"

Oxymercuration

-Common Solvents: Hg(OAc)₂/NaBH₄ (water as nucleophile)

-Mechanism: Break π bond, add OH to more substituted side and H to less substituted side.

-Markovnikov

-Anti addition

-Bridged intermediate forms.

Alkoxymercuration

-Common Solvents: Hg(OAc)₂/NaBH₄ (alcohol as nucleophile) -Mechanism: Break π bond, add O-R group to more substituted side.

-Anti addition

-Markovnikov

-Bridged intermediate forms.

Hydroboration

-Syn addition

-Anti-Markovnikov

- Common Solvents: BH₃/THF, NaOH/H₂O or BH₃/THF → HOOH, OH⁻ (oxidation step)

-Mechanism: Break π bond, add OH to less substituted C and H to more substituted C.

Epoxidation

-Common Solvents: Peroxyacid (e.g., mCPBA) (these usually have an -OOH group.)

-Mechanism: Break π bond, skewers O atom onto double bond.

-Syn addition

-Hydrolysis for diol formation

Dihydroxylation

-Syn addition (unless mCPBA/H₃O⁺ used)

- Common Solvents: KMnO₄ → Diol formation; OsO₄ + H₂O → Diol formation

- Mechanism: Add OH groups to both sides of broken π bond.

Ozonolysis/Oxidative Cleavage

-Common Solvents: O₃/ZnCl or CH₃SCH₃

-Mechanism: Split double bond and add O atoms to both sides. For cyclic compounds, unfold the ring.

Cyclopropanation

-Syn addition

-Common Solvents: CH₂I₂/Zn(Cu)

-Mechanism: Break π bond and form cyclopropane ring by adding CH₂ across it.

HC☰CH

Acetylene

NH2

takes beta H/deprotonates (Strong base)

-if there's 3 equiv, it takes 3 H's

LiNH3

Takes H/ deprotonates

NaOH

Takes H.

-If substrate has Lv and Nu: on same molecule, epoxide forms

B2H6 (BH3)/THF+H2O2/OH=

Antimark. H-anti OH- side with most H's (less substituted)

E2 Bases

-Strong base removes β-H, antiperiplanar elimination forms double bond

-Hoffman product if kotbu/chickenfoot

Br2/CHCl4 + Br2/H2O=CHCl4

-Anti-addition of Br to alkene.

-H2O: Anti-addition, Br on less subbed, OH on more subbed carbon.

H+

-The π electrons in the double bond of the alkene act as a Nu: and attack the H+ (electrophile).

-This breaks the double bond and forms a carbocat intermediate.

-The carbon that becomes positively charged is typically the one that leads to the most stable carbocation

if a peroxide is present, or if the reaction occurs in the light, then the hydrohalogenation product is (anti markovnikov/markovnikov)

anti markovnikov