[Campbells Pawn]

After studying Benzene at A-Level, I have been wondering if there are any similar compounds that have similar properties but with different molecular formulas, say a larger, C8H8 or a C4H4? My teacher hinted at the possibility of a compound containing 4 delocalised electrons.

Have any of these, 'sister compounds' been documented or found?

[chenbeier]

Yes.  Check law of Hückel and aromaticity.

[spirochete]

Some links: https://www.masterorganicchemistry.com/2017/01/20/introducing-aromaticity/

https://www.masterorganicchemistry.com/2017/03/27/antiaromaticity/

And there are also many others when you search for "aromaticity." This will be covered in depth in college level organic chemistry, and even further in depth in other chemistry classes such as physical chemistry.