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Chapter 4 Ketones and Aldehydes

Chapter 4 Ketones and Aldehydes. =>. 4.1 Carbonyl Structure. Carbon is sp 2 hybridized. C=O bond is shorter, stronger, and more polar than C=C bond in alkenes. 4.2 Carbonyl Compounds. =>. 4.3 Naming Aldehydes. IUPAC: Replace - e with - al . The aldehyde carbon is number 1.

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Chapter 4 Ketones and Aldehydes

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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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