Book Cover Organic Chemistry 4e Carey
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Chapter 16: Ethers, Epoxides and Sulfides



Summary | Ethers | Preparations of Ethers | Reactions of Ethers | Epoxides | Preparation of Epoxides | Reactions of Epoxides | Spectroscopic Analysis of Ethers | Sulfides | Self Assessment | Quiz |


Preparation of Epoxides

Chapter 16: Ethers, Epoxides and Sulfides

Epoxidation of Alkenes
(review of Chapter 6)

epoxidation of alkenes
Reaction type: Electrophilic Addition

Summary.

Question:
What other addition reactions convert an alkene into a product with a three membered ring ? Simmons-Smith reaction to a cyclopropane (see Ch 14)

Related reactions


 
MECHANISM FOR REACTION OF ALKENES WITH PERACID
A single step reaction involving several changes. Start at the C=C as the nucleophile, make a bond to the slightly electrophilic O, break the weak O-O bond and form a C=O, break the original C=O to make a new O-H bond, break the original O-H to form the new C-O bond ! (phew !) formation of an epoxide by reaction of a peracid with an alkene

Using Halohydrins to Synthesize Epoxides
(review of Chapter 6 and 8)

preparation of a 1,2-halohydrin
intramolecular S<sub>N</sub>2 to give an epoxide
Reaction type: Electrophilic Addition then Nucleophilic Substitution

Summary

Questions:
What named reaction is the ring closure step most like ? Williamson ether synthesis
If the ring closure is an SN2 reaction then what should be the arrangement of the -O-C-C-X system ?180 degrees = anti (recall S<sub>N</sub>2 backside attack, see Ch8)
What is the stereochemistry of the halohydrin formation ?anti : water opens the halonium ion (review Ch6 on halohydrins)

Related reactions

MECHANISM OF HALOHYDRIN TO EPOXIDE
Step 1:
An acid/base reaction.  The base deprotonates the alcohol forming an alkoxide intermediate that has enhanced nucleophilicity.
Friedel-Crafts alkylation of benzene
Step 2:
An SN2 reaction where the alkoxide nucleophile attacks the electrophilic C displacing the leaving group, the halide ion. The nucleophile has to attack anti to the C-X bond.


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