How do I decide the parent chain of an organic compound that has a ring as well as a side chain while naming the compound? I think that this is decided by the number of carbon atoms. The part which has greater the number of carbon atoms, is considered the parent chain. But this fact is not leading to the correct result always. Are there some rules that govern this fact besides the number of carbon atoms.
If you have a simple chain with carbon atoms and an aromatic ring, the priority has the ring, not matter how the chain is long. This rule is NOT valid when you have a functional group: if it is in the linear chain, it has the priority, and the numeration starts from the carbon more near at the functional group, for example
$\ce{CH3-CH2-CO-CH2-CH2-CH3}$. The numeration starts from left, so you write hexan-3-one.