The question appears to refer to the prefix "iso-" in organic chemistry nomenclature, specifically its use in naming isomers of alkanes. Therefore, the reason "ISO" (or rather, "iso-") is used is to denote a specific structural feature within a molecule.
Here's a more detailed explanation:
The prefix "iso-" in organic chemistry nomenclature indicates a particular type of branched alkane. Specifically, it signifies:
- A methyl group (CH3) is attached to the second carbon atom of a carbon chain. This creates a specific isomeric form of the alkane.
Therefore, "iso-" is used to distinguish this branched isomer from the straight-chain isomer (also known as the normal isomer, denoted by "n-").
Example:
- n-Butane is a straight chain of four carbon atoms.
- Isobutane (also known as 2-methylpropane) is a four-carbon alkane, but with a methyl group attached to the second carbon atom.
Key Considerations:
- The "iso-" prefix is used before the alkane name representing the total number of carbon atoms in the molecule. Thus, isobutane contains four carbon atoms in total.
- While "iso-" was part of older IUPAC nomenclature rules, current IUPAC rules strongly prefer systematic naming (e.g., 2-methylpropane instead of isobutane). However, "iso-" remains commonly used, especially for simple, branched alkanes.
In summary, "iso-" is used as a prefix in the name of an alkane to quickly identify a molecule that has a methyl group attached to the second carbon atom in the chain. This helps differentiate between different structural isomers of the same alkane.
