cis-1,2,3,6-tetrahydro-4-methylphthalic anhydride [1] 1,2,3,6-tetrahydro-4-methylphthalic anhydride [2] 1,2,3,6-tetrahydro-3-methylphthalic anhydride [3] tetrahydromethylphthalic anhydride [4] 1,2,3,6-tetrahydromethylphthalic anhydride [5] tetrahydro-4-methylphthalic anhydride [6] 2,3,5,6-tetrahydro-2-methylphthalic anhydride [7]