Chapter 14 Aldehydes and Ketones Spencer L. Seager Michael R. Slabaugh Jennifer P. Harris

ALDEHYDES AND KETONES The carbonyl group: Aldehydes have at least one hydrogen attached to the carbonyl group. Ketones have two carbons attached to the carbonyl group.

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-bromobutanal2-ethylbutanal

COMMON ALDEHYDES

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-pentanone2-methylcyclohexanone

COMMON KETONES

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.

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.

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).

PHYSICAL PROPERTIES (continued)

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

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

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 (K 2 Cr 2 O 7 ), acetone, and benzaldehyde. After the addition of equal amounts of K 2 Cr 2 O 7, the acetone remains unreacted, whereas the benzaldehyde is oxidized.

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.

ALDEHYDE AND KETONE REACTIONS (continued) In the presence of aldehydes, Benedict’s reagent produces a red precipitate. From left to right, three test tubes containing Benedict’s reagent, 0.5% glucose solution, and 2.0% glucose solution. The addition of Benedict’s reagent from the first tube produces colors (due to the red Cu 2 O) that indicate the amount of glucose present.

ALDEHYDE AND KETONE REACTIONS (continued) The addition of H 2 in the presence of catalysts.

ALDEHYDE AND KETONE REACTIONS (continued) Examples:

ALDEHYDE AND KETONE REACTION MAP

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

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

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

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)

IMPORTANT ALDEHYDES AND KETONES (continued)