Chapter 8: Reactions of Alkenes

Hydrohalogenation

-the addition of HCl or HBr to a multiple bond to give an alkyl halide product

-Markovnikov addition: HBr

-Anti-markovnikov addition: HBR and ROOR

-1 chiral center=pair of enantiomers possible

Acid Catalyzed Hydration

- used to convert alkenes to alcohols

- Markov regioselevtivity

- carbocation rearrangements are possible

- When a new chiral center is generated, a racemic mixture of enantiomers is expected

H20, H+, H2SO4 (aq)

Oxymercuration-Demercuration

-Will not undergo carbocation rearrangements

-Nucleophile attacks the most substituted position

-Markovnikov addition

1. Hg(OAC)2, H20

2. NaBH4

Hydroboration Oxidation

-Anti-Markovnikov addition

-Undergoes Syn addition

-BH2 is installed at less substituted position and OH is installed at the less substituted position

-1 chiral center= racemix mixture

-2 chiral centers= syn addition

1. BH3, THF

2. H202, NaOH

Catalytic Hydrogenation

-reduces alkenes to alkanes

Zero chiral centers: syn requirement is not relevant. Only one product formed

One chiral center: Both possible enantiomers are formed

Two chiral centers: The requirment for syn addition determines which pair of enantiomers is obtained. (Be careful of meso compounds)

1. H2, Ni

Halogenation

-involves the addition of X2 (either Br2 or Cl2) across an alkene.

-For most simple alkenes, halogenation appears to proceed via an anti-addition

-The stereochemical outcome for halogenation reactions is dependent on the configuration of the starting alkene

1. Br2 or Cl2

Halohydrin Formation

-Installs OH at the more substituted position

Anti Dihydroxylation

What's added: OH and OH

Regioselectivity: N/A

Stereoselectivity: anti

Intermediate: don't worry about it

Rearrangement: not possible

anti-addition becomes irrelevant with one chiral center

1. RCO3H

2. H3O+

Syn Dihydroxylation

1. OsO4

2. NaHSO3, H2O

or

1. KMnO4

2. NaOH cold

Oxidative Cleavage

-the C=C bond is completely split apart to form two C=O bonds. Therefore, issues of stereochemistry and regiochemistry become irrelevant.

1. O3

2. DMS or Zn/H20

Oxidative Cleavage by KMNO4

-KMNO4 is a strong oxidizing agent

-If KMNO4 makes a aldehyde it is further oxidized to RCO2H

-IF KMNO4, makes a formaldehydte it is oxidized to formic acid but it decomposes to CO2 which is the final product

Oxidation/Reduction

Oxidation: number of oxygen increases OR number of hydrogen decreases

TsCl, pyridine can be used on a ____and ____alcohol

primary and secondary but not tertiary

Primary alcohol undergoes ____while secondary and tertiary undergo ____

E2, E1 (H2SO4)

Primary alcohol undergoes _____while secondary and tertiary undergo____

SN2, SN1 (HBr)

If FINAL carbons is less than STARTING carbons during synthesis, use...

1) O3

2) DMS