Thymine dimer

Cyclobutadithymine

cis-syn-Thymine dimer

1,4a,4b,8,8aα,8bα-Hexahydro-4aα,4bα-dimethylcyclobuta[1,2-d:4,3-d']dipyrimidine-2,4,5,7(3H,6H)-tetrone

4aβ,4bβ-Dimethyl-4a,4b,8aβ,8bβ-tetrahydrocyclobuta[1,2-d:4,3-d']dipyrimidine-2,4,5,7(1H,3H,6H,8H)-tetrone

5β,6β-[2,4(1H,3H)-Dioxo-5,6-dihydro-5-methylpyrimidine-5α,6α-diyl]-5-methyl-5,6-dihydropyrimidine-2,4(1H,3H)-dione