Firstly, it should be noted that C9H9 is not a complete chemical formula or a specific chemical name. The representation of a chemical formula not only needs to list the number of each type of atom, but also needs to describe the molecular structure. The formula C9H9 simply indicates an organic compound that has 9 carbon atoms and 9 hydrogen atoms, without specifying its structure or its exact name.
One of the substances that could have the formula C9H9 is Indene. Indene is an unsaturated organic hydrocarbon, belonging to the class of compounds including cyclopentadiene and benzene.
Indene is pale yellow in color, has a naphthalene-like smell, and is insoluble in water but soluble in organic solvents such as ethanol and diethyl ether. It is non-acidic, does not create ions, and does not react with metals, salts or nonmetals.
Indene can be synthesized from cyclopentadiene through the process of dimerization and then by removing a hydrogen atom through pyrolysis.
However, as mentioned, C9H9 could represent many different compounds depending on how the carbon and hydrogen atoms are arranged in the molecule. Therefore, you should accurately determine the chemical substance you want to further study.