4 The chemical structure of pesticides

Examples of the pesticides that you will be analysing are given in Table 1.

Table 1  Examples of the class of OCPs
PesticideMolecular formulaStructureInformation Footnotes   a
AldrinC12H8Cl6
Image of chemical structure of Aldrin

pesticide

(banned but restricted use as a local insecticide)

DieldrinC12H8Cl6O
Image of chemical structure of Dieldrin

insecticide

(banned but restricted use for agricultural purposes)

Dichlorodiphenyltrichloroethane (DDT)
Image of chemical structure of Dichlorodiphenyltrichloroethane.

pesticide

(banned but restricted use for malaria control)

EndosulfanC9H6Cl6O3S
Image of chemical strcuture of Endosulfan.

insecticide

(banned only recently, still in use in China and India)

EndrinC12H8Cl6O
Image of chemical structure of Endrin.

insecticide and rodenticide

(banned)

Hexachlorocyclohexane (αHCH)
Image of chemical structure of Hexachlorocyclohexane.

pesticide

(banned)

Lindane (γ-HCH)C6H6Cl6
Image of chemical structure of Lindane.

insecticide

(banned but restricted pharmaceutical use for treatment of lice and scabies)

Heptachlor
Image of chemical structure of Heptachlor

insecticide

(banned but restricted use use as a termiticide)

Methoxychlor
Image of chemical structure of Methoxychlor

insecticide

(banned in US and EU)

Pentachloronitrobenzene (PCNB)C6Cl5NO2
Image of chemical structure of Pentachloronitrobenzene
fungicide

Footnotes  

Footnotes   a Banned status according to the United Nations Treaty (known as the Stockholm Convention on Persistent Organic Pollutants), which has been signed by the majority of countries. One notable exception is the USA, which has its own list of banned substances covering many of the same pesticides.

Look at the pesticide structures in Table 1. Most of these probably look more complicated than the sorts of things you’ve seen before but they follow just the same principles as simpler molecules. To simplify them carbon and hydrogen atoms aren’t labelled in these skeletal structures, but we need to remember them. To get a feel for this, Figure 3 shows two alternative ways of depicting a benzene ring, with the structure on the right corresponding to the method used for the pesticide structures in the Table.

Figure 3  Alternative ways of depicting a benzene ring © The Open University
The benzene ring contains six carbon atoms, each depicted by the letter "C", and joined together by alternating single and double bonds. Single bonds are depicted by a single line, and double bonds by a double line. Each carbon atom is joined by a single bond to a hydrogen atom, depicted by the letter "H". There are six hydrogen atoms in total.
The benzene ring is depicted as a hexagon. Three sides have a second parallel line inside the hexagon so that each point has three lines. Each point represents a carbon atom and each line represents a bond. The diagram shows that each carbon atom has three bonds, and each absent fourth bond must therefore be connected to a hydrogen atom.

3 What you’ll be doing in this investigation

5 The chemical structure of pesticides continued