Nomenclature of Alkanes (IUPAC Rules)

 

Nomenclature of Alkanes (IUPAC Rules):

The IUPAC (International Union of Pure and Applied Chemistry) system provides systematic rules for naming alkanes and other organic compounds. Here are the basic rules for naming alkanes:

Rule 1: Identify the longest continuous carbon chain in the molecule. This chain is referred to as the "parent chain," and its length determines the base name of the molecule (e.g., methane, ethane, propane, etc.).

Rule 2: Number the carbon atoms in the parent chain starting from the end that gives the lowest possible number to the substituents (groups attached to the main chain). This ensures that the substituent's position is as low as possible in the name.

Rule 3: If the molecule has identical substituents, they are listed only once in the name, but a prefix is used to indicate how many of them are present (e.g., di-, tri-, tetra-). For example, "2,2-dimethylbutane" means there are two methyl groups attached to carbon atom 2 in the butane chain.

Rule 4: When the molecule has additional branches (side chains), these branches are named as alkyl groups, and their positions are indicated by numbers corresponding to their attachment point on the parent chain. Complex alkyl groups are enclosed in parentheses to avoid confusion.

Rule 5: When numbering the chain produces two possible sets of numbers, the set that gives the lowest individual number at the first point of difference is chosen.

·         Example:
For the molecule 4,4,5-triethyl-3,5-dimethyloctane:

o    The parent chain is "octane" (8 carbons).

o    There are three ethyl groups attached at positions 4, 4, and 5.

o    There are two methyl groups attached at positions 3 and 5.