Structurally the only difference between JWH-133 and dimethylbutyl-D8-THC is that JWH-133 lacks the hydroxy group seen on dimethylbutyl-D8-THCs phenol structure (the C1 position of the A ring), turning this group into a phenyl (JWH-133) instead of phenol.
The chemical difference between JWH-133 and dimethylbutyl-D8-THC is that JWH-133 lacks the hydroxyl group found on the phenol structure of dimethylbutyl-D8-THC, replacing it with a phenyl group at the C1 position of the A ring.