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Aldehydes and Ketones: Structures, Naming, and Reactions

Explore the structure, nomenclature, and properties of aldehydes and ketones with examples and common names. Discover the industrial significance and preparation methods of these carbonyl compounds. Learn about their physical properties, isomerism, and reactions.

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Aldehydes and Ketones: Structures, Naming, and Reactions

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  1. Chapter 4Ketones and Aldehydes

  2. => 4.1 Carbonyl Structure • Carbon is sp2 hybridized. • C=O bond is shorter, stronger, and more polar than C=C bond in alkenes. Chapter 18

  3. 4.2 Carbonyl Compounds => Chapter 18

  4. 4.3 Naming Aldehydes • IUPAC: Replace -e with -al. • The aldehyde carbon is number 1. • If -CHO is attached to a ring, use the suffix -carbaldehyde. • There are no cycloaldehydes => Chapter 18

  5. Examples 3-methylpentanal 2-cyclopentenealdehyde => benzaldehyde - aromatic => Chapter 18

  6. Small unbranched aldehyde common names • Use the common name of the acid. • Drop -ic acid and add -aldehyde. • 1 C: formic acid, formaldehyde • 2 C’s: acetic acid, acetaldehyde • 3 C’s: propionic acid, propionaldehyde • 4 C’s: butyric acid, butyraldehyde. => Chapter 18

  7. 4.4 IUPAC Names for Ketones • Replace -e with -one. Indicate the position of the carbonyl with a number. • Number the chain so that carbonyl carbon has the lowest number. • For cyclic ketones the carbonyl carbon is assigned the number 1.=> Chapter 18

  8. Examples 3-methyl-2-butanone 3-bromocyclohexanone 4-hydroxy-3-methyl-2-butanone => Chapter 18

  9. O C H C H2 C C H C H 3 3 C H 3 Common Names for Simple Ketones • Named as alkyl attachments to -C=O. methyl isopropyl ketone ethyl isopropyl ketone => Chapter 18

  10. Historical Common Names acetophenone acetone benzophenone => Chapter 18

  11. Name as Substituent • On a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl. • Aldehyde priority is higher than ketone. 3-methyl-4-oxopentanal 3-formylbenzoic acid => Chapter 18

  12. 4.5 Isomerism in aldehydes and ketones • Aldehydes and ketones are constitutional isomers • Aldehydes and ketones can have skeletal and positional isomers if there are enough carbons. • Stereoisomers are also possible if there is a ring or C=C in the molecule Chapter 18

  13. 4.6 Selected Common aldehydes and ketones • Formaldehyde • Acetone • Vanillin • Benzaldehyde • Cinnamaldehyde • Butanedione Chapter 18

  14. formaldehyde, b.p. -21C formalin trioxane, m.p. 62C => Formaldehyde • Gas at room temperature. • Formalin is a 40% aqueous solution. Chapter 18

  15. Industrial Importance • Acetone and methyl ethyl ketone are important solvents. • Formaldehyde used in polymers like Bakelite. • Flavorings and additives like vanilla, cinnamon, artificial butter. => Chapter 18

  16. Formaldehyde -formalin • Acetone – solvent and metabolic product • Vanillin - vanilla flavoring • Benzaldehyde - almond flavor • Cinnamaldehyde - cinnamon • Butanedione - butter Chapter 18

  17. 4.7 Physical properties • Boiling points – page 121 • Solubility – water solubility page 123 Chapter 18

  18. => Boiling Points • More polar, so higher boiling point than comparable alkane or ether. • Cannot H-bond to each other, so lower boiling point than comparable alcohol. Chapter 18

  19. Solubility • Good solvent for alcohols. • Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O-H or N-H. • Acetone and acetaldehyde are miscible in water. => Chapter 18

  20. 4.8 Preparation of Aldehydes and Ketones • Oxidation • 2 alcohol + Na2Cr2O7  ketone • 1 alcohol  aldehyde Chapter 18

  21. 4.9 Oxidation and reduction of Aldehydes and ketones Chapter 18

  22. => Chapter 18

  23. => Tollens Test • Add ammonia solution to AgNO3 solution until precipitate dissolves. • Aldehyde reaction forms a silver mirror. Chapter 18

  24. Oxidation of ketones Ketones  no reaction Chapter 18

  25. O H O H2 / Ni H2 / Ni CH3CHO CH3CH2OH H Reduction – Catalytic Hydrogenation • Ketones give secondary alcohols • Aldehydes give primary alcohols Chapter 18

  26. Reduction: aldehyde + hydrogen --> pri. Alcohol • Form of addition reaction. Chapter 18

  27. Reduction: aldehyde + hydrogen • Break hydrogen bond Chapter 18

  28. Reduction: aldehyde + hydrogen • Break double bond and use electrons to bond with hydrogen. Chapter 18

  29. Reduction: aldehyde + hydrogen • Brief Method Chapter 18

  30. 4.10 Addition of Alcohol • Hemiacetal and Acetal Functional Groups Chapter 18

  31. Hemiacetal and Acetal Functional Groups • Hemiacetal: alcohol and ether on same carbon • Acetal: Two ethers on same carbon Chapter 18

  32. 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. => Chapter 18

  33. Hemiacetal Synthesis: aldehyde + alcohol • Alcohol + aldehyde --> hemiacetal • Ethanal + methanol • Alcohol oxygen becomes an ether • Carbon double bond oxygen becomes an alcohol Chapter 18

  34. => Mechanism for Hemiacetal Chapter 18

  35. Aldehyde and Ketone Reactions Chapter 18

  36. Synthesis of Acetal Functional Group • Acetal: alcohol plus hemiacetal (ether synthesis) • Acetal: Two ethers on same carbon Chapter 18

  37. => Chapter 18

  38. Aldehyde and Ketone Reactions Chapter 18

  39. => Mechanism Hemiacetal to Acetal Chapter 18

  40. => Cyclic Acetals • Addition of a diol produces a cyclic acetal. • Sugars commonly exist as acetals or hemiacetals. Chapter 18

  41. SKIP 4.11 AND 4.12 THE END Chapter 18

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