IUPAC Nomenclature Rules

The IUPAC establishes in decreasing order of hierarchy the nomenclature rules for functional groups and their prefixes.

Functional Groups Priority Table

Priority of Functional Groups

When a compound has more than one functional group, the following rules apply:

1. The highest priority group is indicated with a suffix (following the order in the table).
2. Lower priority groups are indicated with prefixes.
3. Numbering starts from the end closest to the main group.

Examples of compounds with multiple functional groups:

4-hydroxybutanoic acid:

Contains a carboxylic acid group (-COOH) and an alcohol group (-OH). The carboxylic acid has higher priority and is indicated with the suffix "-oic". The alcohol, of lower priority, is indicated with the prefix "hydroxy-".

4-oxopentanal:

Contains an aldehyde group (-CHO) and a ketone group (=O). The aldehyde has higher priority and is indicated with the suffix "-al". The ketone, of lower priority, is indicated with the prefix "oxo-".

4-aminobutanoic acid:

Contains a carboxylic acid group (-COOH) and an amine group (-NH₂). The carboxylic acid has higher priority and is indicated with the suffix "-oic". The amine, of lower priority, is indicated with the prefix "amino-".

Characteristics of Functional Groups

Functional groups confer specific physical and chemical properties to organic molecules:

Alcohols (-OH)

Key property: Form hydrogen bonds, increasing water solubility. Example: Ethanol (CH₃CH₂OH) - component of alcoholic beverages, water soluble.

Carboxylic acids (-COOH)

Key property: Acidic behavior, donate protons in aqueous solution. Example: Acetic acid (CH₃COOH) - component of vinegar, acidic pH.

Aldehydes (-CHO)

Key property: Very reactive with alcohols, form hemiacetals and acetals. Example: Glucose - in aqueous solution it cyclizes forming hemiacetals.

Amides (-CONH₂)

Key property: Peptide bonds, stability, hydrogen bonding. Example: Urea (NH₂CONH₂) - final product of protein metabolism.

Ketones (=O)

Key property: More stable than aldehydes, moderate polarity. Example: Acetone (CH₃COCH₃) - common solvent, present in nail polish removers.

Esters (-COOR)

Key property: Pleasant aromas and flavors, less polar than acids. Example: Ethyl acetate (CH₃COOCH₂CH₃) - fruity smell, paint solvent.

Amines (-NH₂)

Key property: Basic behavior, capture protons. Example: Methylamine (CH₃NH₂) - smell of rotting fish.

Nitriles (-C≡N)

Key property: High polarity, precursors of acids and amides. Example: Acetonitrile (CH₃CN) - polar aprotic solvent.