Case Western Reserve University Chapter 4 Reactions of Alkenes Organic Chemistry 4th Edition Paula Yurkanis Bruice Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall

Electrophilic Addition of Alkenes

Addition of Hydrogen Halides

What is the product?

Carbocation formation is the rate-limiting step a more stable carbocation

Carbocation Stabilities

Alkyl groups decrease the concentration of positive charge in the carbocation

Delocalization of Electrons

Molecular Orbital Diagram in a Hyperconjugation System

Hammond postulate: the transition state will be more similar to the species that it is closer to energetically Exergonic reaction: early transition state Endergonic reaction: late transition state

I: early transition state III: later transition state II: mid-transition state

Reaction Rate and DG‡ more stable transition state lower DG‡ faster reaction rate

Markovnikov’s Rule The electrophile adds to the sp2 carbon that is bonded to the greater number of hydrogens In a regioselective reaction, one constitutional isomer is the major or the only product

tert-Butyl cation is formed faster and it is more stable

Addition of Water to Alkene

Hydration of Propene

Acid-Catalyzed Addition of Alcohol

Rearrangement of Carbocation 1,2-hydride shift a more stable carbocation

Rearrangement of Carbocation a more stable carbocation 1,2-methyl shift

Carbocation does not always rearrange …

Carbocation Rearrangement Ring Expansion a more stable carbocation

Addition of Halogens to Alkene

in the Presence of Water Addition of Halogens in the Presence of Water

Consider the transition states …

Oxymercuration and Mercuration of Alkene

Demercuration by Reduction

Hydroboration–Oxidation Addition of Borane Hydroboration–Oxidation Anti-Markovnikov’s rule in product formation

Anti-Markovnikov addition Markovnikov addition (a pericyclic reaction)

Formation of Alkyl Boranes

OH Replacement of Boron

Anti-Markovnikov Addition of an OH Group

Reaction of Carbene with Alkene

Synthesis of Bromobutane

Generation of Radicals

Addition of Radicals to Alkene

Relative Stabilities of Alkyl Radicals

Calculating the Change in H°

Addition of Hydrogen to Alkenes

Catalytic Hydrogenation of an Alkene

Potential Energies of Pentene Isomers

Relative Stabilities of Alkenes

Steric Strain in Alkenes

Relative Stabilities of Dialkyl-Substituted Alkenes