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Lecture Organic chemistry - Chapter 17: Aldehydes and ketones

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Chapter 17 provides knowledge of aldehydes and ketones. In this chapter, the following content will be discussed: Nomenclature, systematic naming (IUPAC), structure, synthesis, reactions, hydration: geminal diols,.and other contents. | Chapter 17: Aldehydes and Ketones Functional Group: Carbonyl Aldehyde: RCHO, Ketone: RCOR’, 10/5/2014 © Univesity of California 1 Nomenclature The carbonyl group of aldehydes and ketones has priority over all other polar or functions used so far, namely RX, ROH, , , (But not COOH— to be covered later) > In addition: Systematic Naming (IUPAC) Aldehydes Alkane Alkanal. Longest chain starts at -CH=O, which contains C1. Examples: Formaldehyde Acetaldehyde IUPAC-accepted common names Cyclic aldehydes have the ending -carbaldehyde after cycloalkane name. The carbon attached to -CH=O is C1. Examples: The unit as a substituent is called formyl. Cis-2-ethenylcyclo-hexanecarbaldehyde ● ● ● Ketones Alkane Alkanone. Longest chain incorporates carbonyl carbon and is numbered from terminus close to C=O. Cyclic ketones are cycloalkanones; C=O is C1. Examples: 2-Pentanone An aldehyde containing a ketone C=O is called an oxoalkanal. Example: Substituent name: acyl O R O CH3 acetyl, but propanoyl | Chapter 17: Aldehydes and Ketones Functional Group: Carbonyl Aldehyde: RCHO, Ketone: RCOR’, 10/5/2014 © Univesity of California 1 Nomenclature The carbonyl group of aldehydes and ketones has priority over all other polar or functions used so far, namely RX, ROH, , , (But not COOH— to be covered later) > In addition: Systematic Naming (IUPAC) Aldehydes Alkane Alkanal. Longest chain starts at -CH=O, which contains C1. Examples: Formaldehyde Acetaldehyde IUPAC-accepted common names Cyclic aldehydes have the ending -carbaldehyde after cycloalkane name. The carbon attached to -CH=O is C1. Examples: The unit as a substituent is called formyl. Cis-2-ethenylcyclo-hexanecarbaldehyde ● ● ● Ketones Alkane Alkanone. Longest chain incorporates carbonyl carbon and is numbered from terminus close to C=O. Cyclic ketones are cycloalkanones; C=O is C1. Examples: 2-Pentanone An aldehyde containing a ketone C=O is called an oxoalkanal. Example: Substituent name: acyl O R O CH3 acetyl, but propanoyl (IUPAC accepted common name) O CH3CH2 10/5/2014 © Univesity of California 6 Structure Orbitals The carbonyl group contains a short, strong, and very polar bond. Resonance Polarization Molecular structure Electrostatic Potential Map 175 kcal mol-1 10/5/2014 © Univesity of California 7 Synthesis (A review of Chapter 8) Old: Oxidation of Alcohols Primary aldehydes Secondary ketones Use chromium(VI) reagents (CrO3, Na2Cr2O7) Selective: Will not oxidize alkene or alkyne units. Especially mild is PCC: Pyridine Pyridinium chlorochromate : “PCC” NH + N CrO3Cl - PCC avoids water, which causes overoxidation of primary alcohols Examples: New: Allylic Oxidation with MnO2 Selective: Will not attack ordinary alcohols Allylic H is reactive Not allylic 3. Old: Ozonolysis of Alkenes: O3, then reducing agent [(CH3)2S or Zn, CH3COOH] Oxidative cleavage of carbon-carbon double bonds 4. Old: Hydration of Alkynes Hydration of the carbon–carbon triple bond yields enols that tautomerize to carbonyl .