Alcohols, Ethers and Epoxides. Introduction—Structure and Bonding. Alcohols contain a hydroxy group (OH) bonded to an sp 3 hybridized carbon. Compounds having a hydroxy group on a sp 2 hybridized carbon— enols and phenols —undergo different reactions than alcohols.
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Alcohols, Ethers and Epoxides
Introduction—Structure and Bonding
Nomenclature of Ethers
Nomenclature of Epoxides
Preparation of Alcohols, Ethers, and Epoxides
Reactions of Alcohols
Reactions of Alcohols—Dehydration
Consider the example below. 2° Carbocation A rearranges to the more stable 3° carbocation by a 1,2-hydride shift, whereas carbocation B does not rearrange because it is 3° to begin with.
Dehydration of Alcohols Using POCl3 and Pyridine
Conversion of Alcohols to Alkyl Halides with HX
Conversion of Alcohols to Alkyl Halides with SOCl2 and PBr3
Tosylate—Another Good Leaving Group
substitution and βelimination
reactions of alcohols
Reaction of Ethers with Strong Acid
Example: In the reaction of (CH3)3COCH3 with HI, the 3° alkyl group undergoes nucleophilic substitution by an SN1 mechanism, resulting in the cleavage of one C—O bond. The methyl group undergoes nucleophilic substitution by an SN2 mechanism, resulting in the cleavage of the second C—O bond.
Reactions of Epoxides
Consider the following real examples:
Let’s now consider the stereochemical consequences of the reaction of 1,2-epoxycyclohexane with ¯OCH3.
Nucleophilic attack of ¯OCH3 occurs from the backside at either C—O bond, because both ends are similarly substituted. Since attack at either side occurs with equal probability, an equal amount of the two enantiomers (i.e., a racemic mixture) is formed.
Optically inactive starting materials give optically inactive products!
Opening of an unsymmetrical
epoxide ring with HCI