Organic Chemistry: Aldehydes and Carbonyl Group

Carbonyl Group

• The carbonyl group consists of a carbon atom bonded to three other atoms by sigma bonds, forming a plane with 120° angles.
• The remaining p orbital of the carbon overlaps a p orbital of oxygen to form a pi bond, resulting in a double bond between carbon and oxygen.
• The electrons of the carbonyl double bond are not equally shared, with the mobile pi cloud pulled strongly toward the more electronegative oxygen atom.

Structure of Aldehydes

• In an aldehyde, the carbon of the carbonyl group is bonded to at least one hydrogen atom.
• The carbon may also be bonded to another hydrogen atom, a carbon of an alkyl group (aliphatic compound), or an aromatic ring.
• The carbonyl group can be drawn as separate atoms or written as (-CHO) in condensed structural formulas.

Nomenclature of Aldehydes

• Aldehydes are named by replacing the (e) of the corresponding alkane name with (-al) in the IUPAC system.
• The suffix "-al" indicates the presence of an aldehyde group.
• The parent chain is selected by identifying the longest chain that includes the carbon atom of the aldehydic group.
• The aldehydic carbon is assigned number 1 when numbering the parent chain.

Physical Properties of Aldehydes

• At room temperature, methanal (formaldehyde) and ethanal (acetaldehyde) are gases.
• Aldehydes with 3 to 10 carbon atoms are liquids.
• The polar carbonyl group influences the boiling points and solubility of aldehydes in water.
• The boiling points of aldehydes increase as the number of carbon atoms in the chain increases.
• Aldehydes with 1 to 4 carbon atoms are very soluble in water, while those with 5 or more carbon atoms are not very soluble.

Reactions of Aldehydes

• Aldehydes produced by the oxidation of primary alcohols oxidize readily to carboxylic acids.
• Aldehydes are reduced by hydrogen to form primary alcohols, requiring a catalyst such as nickel, platinum, or palladium.

Learn about the structure and properties of aldehydes, including the carbonyl group, naming conventions, and physical properties. Quiz covers aliphatic and aromatic aldehydes.