ALDEHYDES AND KETONES

2. ALDEHYDES AND KETONES • The carbonylgroup: • Aldehydes have at least one hydrogen attached to the carbonylgroup. • Ketones have two carbons attached to the carbonylgroup.

3. NAMING ALDEHYDES • Find the longest carbon chain that contains the aldehyde group. • Change ending of the root hydrocarbon name by dropping –e and adding –al. • All other branches and groups are named and located using standard IUPAC system. • Examples: 3-bromobutanal 2-ethylbutanal

4. COMMON ALDEHYDES

5. NAMING KETONES • Find the longest chain that contains C=O. • Using the root alkane name, drop the –e ending and change to –one. • Number the longest carbon chain so the C=O group has the lowest number. • Name and number other substituents as before. • Examples: 3-methyl-2-pentanone 2-methylcyclohexanone

6. COMMON KETONES

7. PHYSICAL PROPERTIES • The carbonyl group is moderately polar, but it doesn’t have any hydrogen atoms bonded to the oxygen atom, so it cannot hydrogen bond between molecules.

8. PHYSICAL PROPERTIES (continued) • Because of the polarity of the C=O group, these groups can interact, but the attraction is not as strong as hydrogen bonding. • This makes the boiling point of aldehydes and ketones higher than alkanes, but lower than alcohols.

9. PHYSICAL PROPERTIES (continued)

10. PHYSICAL PROPERTIES (continued) • The C=O group can hydrogen bond with water molecules because the oxygen atom in the carbonyl group has a partial negative charge that attracts the partial positive charge of a hydrogen atom in the water molecule. • This makes low molecular weight aldehydes and ketones water soluble (they have small hydrophobic sections).

11. PHYSICAL PROPERTIES (continued)

12. ALDEHYDE AND KETONE REACTIONS • Recall the oxidation of alcohols to produce aldehydes and ketones:

13. ALDEHYDE AND KETONE REACTIONS (continued) • The difference in reactivity toward oxidation is the chief reason why aldehydes and ketones are classified in separated families.

14. ALDEHYDE AND KETONE REACTIONS (continued) • The ease with which aldehydes are oxidized allows us to test for the presence of aldehydes with Tollens’ reagent or Benedict’s reagent. • In general, ketones fail to react with these reagents. From left to right, three test tubes containing potassium dichromate (K2Cr2O7), acetone, and benzaldehyde. After the addition of equal amounts of K2Cr2O7, the acetone remains unreacted, whereas the benzaldehyde is oxidized.

15. ALDEHYDE AND KETONE REACTIONS (continued) • In the presence of aldehydes, Tollens’ reagent produces a silver coating on glass. • This method is used to produce mirrors and silver ornaments.

16. ALDEHYDE AND KETONE REACTIONS (continued) • In the presence of aldehydes, Benedict’s reagent produces a red precipitate. The addition of Benedict’s reagent from the first tube produces colors (due to the red Cu2O) that indicate the amount of glucose present. From left to right, three test tubes containing Benedict’s reagent, 0.5% glucose solution, and 2.0% glucose solution.

17. ALDEHYDE AND KETONE REACTIONS (continued) • The addition of H2 in the presence of catalysts.

18. ALDEHYDE AND KETONE REACTIONS (continued) • Examples:

19. ALDEHYDE AND KETONE REACTION MAP

20. IMPORTANT ALDEHYDES AND KETONES • Formaldehyde • Gas at room temperature • Formalin – 37% aqueous solution • Sterilizer • Embalming fluid • Starting material for plastics such as Formica and Bakelite

21. IMPORTANT ALDEHYDES AND KETONES (continued) • Acetone • Important organic solvent • Used in such things as nail polish remover • Miscible with water

22. IMPORTANT ALDEHYDES AND KETONES (continued) • Progesterone and testosterone (female and male sex hormones) are ketones.

23. IMPORTANT ALDEHYDES AND KETONES (continued) • Some aldehydes and ketones are very fragrant and are used in flavorings. • Vanillin (vanilla) • Cinnamaldehyde (cinnamon) • Citral (citrus flavoring) • Camphor (medicinal odor)

24. IMPORTANT ALDEHYDES AND KETONES (continued)

25. IMPORTANT ALDEHYDES AND KETONES (continued)