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Understanding Ketones and Aldehydes: Naming, Properties, Reactions

Explore IUPAC naming, solubility, historical names, synthesis, reactions, industrial importance, and more in organic chemistry. Learn about the addition of water, HCN, hemiacetals, and Tollens test in the context of carbonyl compounds.

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Understanding Ketones and Aldehydes: Naming, Properties, Reactions

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  1. Organic Chemistry, 6th EditionL. G. Wade, Jr. Chapter 18Ketones and Aldehydes

  2. Carbonyl Compounds => Chapter 18

  3. 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

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

  5. Naming Aldehydes • IUPAC: Replace -e with -al. • The aldehyde carbon is number 1. • If -CHO is attached to a ring, use the suffix -carbaldehyde. => Chapter 18

  6. Examples 3-methylpentanal 2-cyclopentenecarbaldehyde cyclopent-2-en-1-carbaldehyde => Chapter 18

  7. 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

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

  9. => 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

  10. 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

  11. 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

  12. Synthesis Review • Oxidation • 2 alcohol + Na2Cr2O7  ketone • 1 alcohol + PCC  aldehyde • Friedel-Crafts acylation Acid chloride/AlCl3 + benzene  ketone Chapter 18

  13. => Nucleophilic Addition • A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated. • A weak nucleophile will attack a carbonyl if it has been protonated, thus increasing its reactivity. • Aldehydes are more reactive than ketones. Chapter 18

  14. => Addition of Water • In acid, water is the nucleophile. • In base, hydroxide is the nucleophile. Chapter 18

  15. => Addition of HCN • HCN is highly toxic. • Use NaCN or KCN in base to add cyanide, then protonate to add H. • Reactivity formaldehyde > aldehydes > ketones >> bulky ketones. Chapter 18

  16. => Formation of Imines • Nucleophilic addition of ammonia or primary amine, followed by elimination of water molecule. • C=O becomes C=N-R Chapter 18

  17. Other Condensations => Chapter 18

  18. Addition of Alcohol => Chapter 18

  19. 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

  20. Mechanism for Hemiacetal • Oxygen is protonated. • Alcohol is the nucleophile. • H+ is removed. => Chapter 18

  21. => Hemiacetal to Acetal Chapter 18

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

  23. => Acetals as Protecting Groups • Hydrolyze easily in acid, stable in base. • Aldehydes more reactive than ketones. Chapter 18

  24. => Selective Reaction of Ketone • React with strong nucleophile (base). • Remove protective group. Chapter 18

  25. Oxidation of Aldehydes Easily oxidized to carboxylic acids. => Chapter 18

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

  27. Reduction Reagents • Sodium borohydride, NaBH4, reduces C=O, but not C=C. • Lithium aluminum hydride, LiAlH4, much stronger, difficult to handle. • Hydrogen gas with catalyst also reduces the C=C bond. => Chapter 18

  28. => Catalytic Hydrogenation • Widely used in industry. • Raney nickel, finely divided Ni powder saturated with hydrogen gas. • Pt and Rh also used as catalysts. Chapter 18

  29. End of Chapter 18 Chapter 18

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