1. Hemiacetal and Acetal Functional Groups Hemiacetal: alcohol and ether on same carbon Acetal: Two ethers on same carbon

2. Mechanism Must be acid-catalyzed. Adding H + to carbonyl makes it more reactive with weak nucleophile, ROH. Hemiacetal forms first, then acid-catalyzed loss of water, then addition of second molecule of ROH forms acetal. All steps are reversible. =>

3. Hemiacetal Synthesis: aldehyde + alcohol Alcohol + aldehyde --> hemiacetal Ethanal + methanol Alcohol oxygen becomes an ether Carbon double bond oxygen becomes an alcohol

4. Mechanism for Hemiacetal =>

5. Aldehyde and Ketone Reactions

6. Synthesis of Acetal Functional Group Acetal: alcohol plus hemiacetal (ether synthesis) Acetal: Two ethers on same carbon

7. =>

8. Aldehyde and Ketone Reactions

9. Mechanism Hemiacetal to Acetal =>

10. Cyclic Acetals Addition of a diol produces a cyclic acetal. Sugars commonly exist as acetals or hemiacetals. =>