Chapter 17.8, Problem DQ

Permethrin and Bifenthrin

Pyrethrin is a natural insecticide obtained from the powdered flower heads of several species of Chrysanthemum. The active substances in pyrethrum, principally pyrethrins I and II, are contact poisons for insects and cold-blooded vertebrates. Although powders made from Chrysanthemum extracts have found widespread use, the active substances in them are destroyed rapidly in the environment. In an effort to develop synthetic compounds as effective as the natural insecticides but with greater biostability, chemists prepared a series of esters related in structure. Among the synthetic pyrethrenoids now in common use in household and agricultural products are permethrin and bifenthrin.

As discussed above, the natural products pyrethrins I and II (not shown) are destroyed rapidly in the environment. One of the key changes in the structures of permethrin and bifenthrin relative to the pyrethrins was the substitution of naturally occurring methyl groups on the alkene with electron withdrawing groups (EWGs) such as chlorine and trifluoromethyl. What reactions of the alkene would the change of methyl groups to EWGs retard?

1. 1. Oxidation of the double bond.
2. 2. Electrophilic addition reactions.
3. 3. Nucleophilic addition reactions.
4. 4. Both 1 and 2.
5. 5. All of the above.