However, the chemical environments encountered en route from the application site to the target generally require differing physicochemical properties, while the unit costs are generally much lower.[1] Agrochemicals typically have a lower number of hydrogen bond donors.[4] For example, over 70% of insecticides have no hydrogen bond donor, and over 90% of herbicides have two or fewer. Desirable agrochemicals have residual activity and persistence of effect lasting up to several weeks to allow large spray intervals. The majority of heterocycles found in agrochemicals are heteroaromatic.[1]