Chapter 15: Aldehydes and Ketones

• Carbonyl group is a functional group that has a carbon atom joined to an oxygen atom by a double bond and a carbonyl compound is a compound containing a carbonyl compound.

• Chemists find it useful to divide carbonyl compounds into two major groups based on their chemical properties.

  • In ^^one group are the aldehydes and ketone^^s, which have similar properties because their carbonyl groups are %%bonded to atoms that do not attract electrons strongly—carbon and hydrogen.%%
  • In the ^^second group are carboxylic acids, esters, and amides (the carboxyl family)^^. The carbonyl-group carbon in these compounds is bonded to an atom (other than carbon or hydrogen) %%that does attract electrons strongly, typically an oxygen or nitrogen atom%%. This second group of carbonyl containing compound.

• The simplest aldehydes and ketones are known by common names (formaldehyde, acetaldehyde, benzaldehyde, and acetone).

  • Aldehydes are named systematically by replacing the final -e in an alkane name with -al and when necessary numbering the chain starting with 1 at the ¬CHO group.
  • Ketones are named systematically by adding -one to the alkane name for saturated ketones and numbering starting with 1 at the end nearer the C=O group.
  • In ketones, the location of the carbonyl group is indicated by placing the number of its carbon between the alkane name and -one.

• Properties of Aldehydes and Ketones Aldehyde and ketone molecules are polar due to the presence of the carbonyl group.

  • Since aldehydes and ketones cannot hydrogen bond with one another, they have lower boiling points than alcohols but higher boiling points than alkanes because of dipole–dipole interactions
  • Common aldehydes and ketones are typically liquids.
  • Simple aldehydes and ketones are water-soluble due to hydrogen bonding with water molecules, and ketones are good solvents for many polar and nonpolar solutes.
  • Many aldehydes and ketones have distinctive odours.
  • Simple ketones are less toxic than simple aldehydes.

• Because ketones cannot be oxidized, treatment with a mild oxidizing agent is used as a test to distinguish between aldehydes and ketones.

  • ^^Tollens’ reagent,^^ which consists of a solution containing silver ion in aqueous ammonia, is the most visually appealing oxidizing agent for aldehydes.
  • Treatment of an aldehyde with this reagent, in which the Ag + ion is the oxidizing agent, rapidly yields the carboxylic acid anion and metallic silver.
  • If the reaction is done in a clean glass container, metallic silver deposits on the inner walls, producing a beautiful shiny mirror.

• A test with another mild oxidizing agent, known as ^^Benedict’s reagent,^^ also relies on reduction of a metal ion to produce visible evidence of the presence of aldehydes.

  • The reagent solution contains blue copper(II) ion, which is reduced to give a precipitate of red copper(I) oxide in the reaction with an aldehyde.

• Addition reaction of aldehydes and ketones is the addition of an alcohol or other compound to the carbon double bond to give a carbon–oxygen single bond.

• Hemiacetal is a compound with both an alcohol-like ¬OH group and an ether like ¬OR group bonded to the carbon atom that was at one time the aldehyde carbonyl carbon.

• Hemiketal is a compound with both an alcohol-like ¬OH group and an ether like ¬OR group bonded to the carbon atom that was at one time the ketone carbonyl carbon.

• Acetal is a compound that has two ether-like ¬OR groups bonded to the same carbon atom of what was once an aldehyde.

• Ketal is a compound that has two ether-like ¬OR groups bonded to the same carbon atom of what was once a ketone.

• Hydrolysis is a reaction in which a bond or bonds are broken and the H¬ and ¬OH of water add to the atoms of the broken bond or bonds.

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