Here's why:

* Organic compounds are defined as compounds containing carbon (C) atoms. Both octane and trimethylpentane are hydrocarbons, meaning they consist solely of carbon and hydrogen (H) atoms.

* Octane has the chemical formula C₈H₁₈, meaning it has eight carbon atoms and eighteen hydrogen atoms.

* Trimethylpentane is a generic name for several isomers (different structural arrangements) of the compound with the formula C₈H₁₈. This means it also contains carbon and hydrogen, making it an organic compound.

Let me know if you have any more questions!