The characteristic reaction of alkenes is addition to the double bond. + A—B C C A C C B Reactions of Alkenes

Reactions involving carbocations: 1. 1.Substitutions via Eliminations via the Additions to Reminder: Reactions of Alkenes CH 3 CH 3

Terms: Driven by ___________ bond making __________sigma bonds. Overall Transformation: C=C to Regioselectivity: Which ____________ a specific group is added to. Stereoselectivity: Whether the addition is ____________ or __________ Nucleophile: pi bond has ______________; reacts with ______________. Electrophile: An electron __________ species, which reacts with electron ________ species. Electrophilic Addition: the _________ophile attacks the ________phile Alkene Addition Terms

___ addition____ addition syn Addition versus anti Addition

General Format: Depending on timing, two different mechanisms are possible: Two Step: Full Carbocation Mechanism 1: Reaction of the C=C with E+  Carbocation 2: Nucleophilic attack. Electrophilic Addition Nu E + E Nu E

One Step: Partial Carbocation Mechanism Simultaneous formation of the two sigma bonds. Tips: 1. 1.Find the electrophile The ____________ attacks the __________. 3. Figure out if carbocations are formed step reaction is_________________ 4.Determine if the new sigma bonds are from the same species - __________ addition. 5.Determine if the two new sigma bonds are from different species - __________ addition. Electrophilic Addition ENu ENu

One Step: Partial Carbocation Mechanism _____________ formation of the two sigma bonds. Tips: Electrophilic Addition ENu ENu

CH 3 CH 2 CH 2 CH 3 HH CH 3 CH 2 C C CH 2 CH 3 CHCl 3, -30°C C C HBr Example

Electrophilic addition of hydrogen halides to alkenes proceeds by _________________ formation of a ______________ intermediate. Mechanism

Electrons flow from the  system of the _______ (electron rich) toward the positively polarized ________ of the hydrogen halide. Mechanism

Free Radical Mechanism: Free Radical Mechanism Br Br H Br Br H

Which mechanism is used for the following reactions? Learning Check

Electrophilic Addition: Hydrogenation: Hydrohalogenation: Hydration: Hydroboration: Alkene Reactions

Halogenation: Halohydration: Hydrohalogenation: Epoxidation: Ozonolysis: Alkene Reactions

Reaction Type: Used for heats of hydrogenation stability. Overall Reaction: H 2 + Alkene  Requires: Metal catalyst Regioselectivity: Stereospecificity: ____________addition products. Hydrogenation

HH C C A B X Y HH Mechanism of Catalytic Hydrogenation

CO 2 CH 3 H 2, Pt Example of syn-Addition CO 2 CH 3 H

When an unsymmetrically substituted alkene reacts with a hydrogen halide, the hydrogen adds to the carbon that has the greater number of hydrogen substituents, and the halogen adds to the carbon that has the fewer hydrogen substituents. Markovnikov's Rule

Occurs due to the formation of the most stable carbocation: Markovnikov rules extend to other additions which don’t involve halides: Markovnikov Example

Br CH 3 CH 2 CHCH 3 CH 2 CH 3 CH 2 CH acetic acid HBr Mechanistic Basis for Markovnikov's Rule: Example 1

Mechanistic Basis for Markovnikov's Rule: Example 2 H CH 3 Cl HCl 0°C

Reactions that are _____ Markovnikov add the hydrogen to the side with the ______ number of hydrogens. ______ is attached to the ________ substituted carbon. Reaction does not go through a __________ intermediate. Anti Markovnikov

Reaction of Alkenes with HBr (no radical formation). Reaction Type: Overall Reaction: HX + Alkenes  Hydrogen Halide Reactivity Order: HI HBr HCl HF (same as ________ order) Regioselectivity: Markovnikov Rule. “For addition of hydrogen halides to alkenes, the H atom adds to the C with ______________ H atoms” meaning it goes through the more stable __________________ intermediate.” Hydrohalogenation

Reaction of Alkenes with HBr (no radical formation). Stereoselectivity: _____, during mechanism, a ________________is formed. Requirements: HBr, ________________________ Hydrohalogenation

Mechanism: Hydrohalogenation H H H CH 3 H + H C CH 3 CH 3 Br - The Bromide ion is _____________ The Carbocation is ________________