Organic Chemistry 4 th Edition Paula Yurkanis Bruice Chapter 4 Reactions of Alkenes Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall
Electrophilic Addition of Alkenes
Addition of Hydrogen Halides
What is the product?
a more stable carbocation Carbocation formation is the rate-limiting step
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 II: mid-transition state III: later transition state
Reaction Rate and G ‡ more stable transition state lower G ‡ faster reaction rate
In a regioselective reaction, one constitutional isomer is the major or the only product Markovnikov’s Rule The electrophile adds to the sp 2 carbon that is bonded to the greater number of hydrogens
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
a more stable carbocation Rearrangement of Carbocation 1,2-methyl shift
Carbocation does not always rearrange …
Carbocation Rearrangement a more stable carbocation Ring Expansion
Addition of Halogens to Alkene
Addition of Halogens in the Presence of Water
Consider the transition states …
Oxymercuration and Mercuration of Alkene
Demercuration by Reduction
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