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Aldehydes and Ketones Carbonyl Compounds • Contain C=O double bond. • Include many classes of compounds. 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. Some common aldehydes and ketones: We will not be learning common nomenclature; you are only responsible for IUPAC. Name the Following: Naming Aldehydes Find the longest carbon chain that contains the aldehyde group. Number from the carbonyl carbon; even in the presence of multiple bond. Change ending of the root alkane name by dropping –e and adding –al. All other branches and groups are named and located using standard IUPAC system. Example: 2. :O: 3. 4. O 5. 4-bromo-3-ethyl hexanal :O: 1. O OH OH : :Br: 1 Name the Following: Naming Ketones 3-bromo-2,5dimethyl-4heptanone :O: 4. 3. : :O: 2. 1. :Br: OH :O: 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. Example: :O: 5. : :Br: Physical Properties The carbonyl group is moderately polar, but it doesn’t have any hydrogens attached, so it cannot hydrogen bond between molecules. Physical Properties, cont. Physical Properties, cont. 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. A Comparison The C=O group can hydrogen bond with water molecules. Make a table in your notes: This makes low molecular weight aldehydes and ketones water soluble (they have small hydrophobic sections). Organic molecules (alkane, haloalkane, alcohol, ether, aldehyde and ketone) on one axis, and the 3 intermolecular forces on the other axis. Then, fill in the table using X’s 2 Important Aldehydes and Ketones Methanal (A.K.A. Formaldehyde) •Gas at room temperature •Formalin – 37% aqueous solution •Sterilizer •Embalming fluid •Formaldehyde is starting material for plastics such as Formica and Bakelite. Important Aldehydes and Ketones, cont. 2-propaonoe (A.K.A. Acetone) Important organic solvent used in such things as nail polish remover. Miscible with water. Important Aldehydes and Ketones, cont. Progesterone and testosterone (female and male sex hormones) are ketones. Some aldehydes and ketones are very fragrant and are used in flavorings. Vanillin (vanilla) Cinnamaldehyde (cinnamon) Citral (citrus flavoring) Camphor (medicinal odor) Reaction Review: Primary alcohol oxidation •A primary alcohol can undergo a two step reaction: –In the first reaction, the alcohol loses two hydrogen atoms to form a carbonyl group on a terminal carbon by an oxidizing agent (O), creating an aldehyde. Samples –In the second reaction, the newly formed aldehyde can undergo further oxidation when the remaining hydrogen one the carbonyl carbon is substituted with a hydroxyl forming a carboxyl group, creating a carboxylic acid. 3 Reaction Review, cont. Secondary alcohol oxidation •A secondary alcohol can only undergo one oxidation –the alcohol loses two hydrogen atoms to form a carbonyl group on an intermediate carbon, creating a ketone. – What about a tertiary alcohol? Oxidation States and Organic Reactions: In each of these reactions, identify the atom that is oxidized by assigning oxidation states. Tollens’ Test In the presence of aldehydes, Tollens’ reagent [containing (Ag(NH3)2)+] produces a silver coating on glass. Tollens’ and Benedict’s Test 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. Benedict’s Test In the presence of aldehydes, Benedict’s reagent (containing CuSO4) produces a red copper precipitate. Benedict’s reagent in comparison to 2 glucose solutions 4 Write the reaction of ethanal with both Tollens’ and Benedict’s reagent; Then, identify the atoms being oxidized and those being reduced. 5