title: Stereochemically controlled photoreactions between two thymine rings.
mesh_terms: D001952:Bridged-Ring Compounds; D003500:Cyclization; D010777:Photochemistry; D013237:Stereoisomerism; D013941:Thymine; D014466:Ultraviolet Rays; D014498:Uracil
chemical_list: D001952:Bridged-Ring Compounds; D014498:Uracil; D013941:Thymine