Ethylbenzene
= Ethylbenzene
{wiki}
<Ethylbenzene> is $\mathrm{C_6H_5CH_2CH_3}$, a benzene ring carrying an ethyl substituent. It shares the formula $\mathrm{C_8H_{10}}$ with the xylene isomers but has different connectivity.
Conversion of its side chain to a vinyl group gives <styrene>, connecting a simple aromatic hydrocarbon with an important polymer starting material. Its benzylic carbon also has reactivity distinct from the ring itself.