Highly Fluorinated 2,2′-Biphenols and Related Compounds: Relationship between Substitution Pattern and Herbicidal Activity

A broad range of halogenated 2,2′-biphenols was tested for applicability as crop protection agents. The activity of these compounds toward four typical pest plants was observed after application by spraying of diluted solutions. Despite their rather simple structure, it was found that the studied compounds reveal a surprisingly high herbicidal impact. To gain a better understanding of the structure–activity relationship, specific sites of the molecule were chemically modified and the core structures thus gradually changed. The influence of the substitution pattern on the herbicidal properties is discussed, and conclusions on the active site of the biphenol structure are drawn. It was observed that type and position of the halogen substituents have a significant influence on the activity of the core structure. The hydroxy functionalities play a crucial role for the effectiveness of the tested compounds. Because the blocking of the hydroxy moiety leads to dramatically deteriorated performances, the presence of these functionalities on the aromatic ring seems to be indispensable.