Hey there! C6H6 is benzene, its a ring structure with alternating double and single bonds.
What makes something have a higher delta H vap? It has to be more stable, and therefore it would take more energy to break the bonds.
Because benzene is a ring with alternating single and double bonds, it can have resonance structures, where the electrons can move around (you can change the locations of the double bonds). This gives benzene a higher enthalpy of vaporization. In addition, this is not something you need to know now, but benzene in an aromatic compound and they are very stable.
Hope this helps!