Structural Formula of Iso Heptane:
Iso heptane is a branched-chain alkane with the chemical formula C7H16. Its structural formula can be represented as:
CH3-CH(CH3)-CH2-CH2-CH2-CH2-CH3
This shows that iso heptane has a total of seven carbon atoms arranged in a straight chain with a methyl group (CH3) attached to the second carbon atom.

Structural Formula of Iso Octane:
Iso octane is another branched-chain alkane with the chemical formula C8H18. Its structural formula is:
CH3-CH2-CH(CH3)-CH2-CH2-CH2-CH2-CH3
In this formula, iso octane contains eight carbon atoms with a methyl group attached to the third carbon atom.

Explanation:
- Iso heptane and iso octane are isomers, meaning they have the same molecular formula but different structural arrangements.
- The branching in these molecules affects their physical properties, such as boiling point and octane rating.
- Iso octane, due to its branching, has a higher octane rating compared to straight-chain octane, making it a valuable component in gasoline to prevent knocking in engines.
- Both iso heptane and iso octane are commonly used as reference compounds in octane rating scales to evaluate the performance of gasoline.