Terbuthylazine

Terbuthylazine is a selective herbicide. Chemically, it is a halogenated triazine; compared with atrazine and simazine, it has a tert-butyl group in place of the isopropyl and ethyl group, respectively. The sim-azine molecule with 2 ethyl groups is symmetric and flat. The threefold substituted triazines have resonance of the free electron pairs, resulting in equivalent mesomeric structures.
Simazine remains active in the soil for 2 to 7 months or longer after application. Atrazine remains in soil for a matter of months and can migrate from soil to groundwater.
Terbuthylazine's HRAC classification is Group C1, Group C, Group 5, as it inhibits photosynthesis at photosystem II.