AbstractThe activities of DNOC, dinoseb, dinoterb and dinosam and the 5‐methyl analogues (I; R = Bus, But, or CHMePrnand R' = Me) of these phenols againstCapsella bursa‐pastoris, Chenopodium album, Senecio vulgaris, Stellaria mediaandRumexspp., and their effects on peas, oats, beet, cabbage and carrots, were investigated by pre‐emergence application to soil. The effects of esterification of these phenols with aliphatic acids, of esterification of dinoterb with dibasic acids, aromatic acids, substituted carbonic acids, and of etherification on activity were investigated. 2‐t‐Butyl phenols and their aliphatic esters proved more active than the corresponding compounds of the other phenols. Acetylation improved the activity of dinoterb and medinoterb. Halogenation reduced the activity of the acetate of dinoterb, but unsaturation of the ester chain enhanced the activity of dinoterb esters. Esterification of dinoterb with aromatic acids, substituted carbonic acids, oxalic and adipic acids, and etherification led to compounds of low activity. In general, all compounds caused little damage to peas and oats. Dinoterb esters damaged cabbage plants. Esters of medinoterb were generally less damaging to crops than were dinote