I know that benzene is an alkene, but what is Isopropylbenzene -- C9H12 ?

4 answers

yes. IT is a cycloalkene.
The trivial name for isopropylbenzene is cumene. It is a substituted benzene.
Therefore cumene is an alkene?
Since benzene is an arene, I would call it that (an arene). Technically, it is an alkene but usually aromatic hydrocarbons are called arenes to distinguish them from their cousins, the straight chain alkenes. And I suspect an organic chemist would fuss at me for even calling them cousins.