Chlorinated bridged biphenyls

The rates of chlorination of bridged biphenyls have also been measured and show the effect of coplanarity on reactivity. Second-order rate coefficients (104A 2) at 25 °C were fluorene (1,700), 9,10-dihydrophenanthrene (170), 1,2 3,4-di-benzocyclohepta-1,3-diene (9.70), 5-methyl-l,2 3,4-dibenzocyclohepta-l,3-diene... 

PCBs represent chlorine derivatives of biphenyl, containing from 1 to 10 atoms of chlorine in a molecule that is expressed as 10 different homologues (Figure 2). Having no ethane bridge between the aromatic rings, as opposed to DDT, PCBs are more stable... 

The base biphenyl has 10 hydrogen atoms four of them (2, 6, 2, 6 ) are near the bridge and are named the a positions, four of them (3, 5, 3, 5 ) are away from the bridge and are named the p positions, and two of them (4, 4 ) are opposite the bridge and are named the y positions. There are three forms for mono-chloro biphenyl, depending on the position of the chlorine atom, and they each have different properties. The PCBs are a set of 210 compounds with 0 to 10 chlorine atoms in a molecule. Monsanto made them under the trade name Aroclor, and they came in a number of mixtures the light Araclor 1221 is basically mono- and di-chloro, the medium Aroclor 1248 is principally tri-, tetra- and penta-chloro, and the heavy Aroclor 1260 is principally hexa- and hepta-chloro. We are concerned with the transportation and concentration of these chemicals, particularly in fish and humans, which are controlled by the three parameters of vapor pressure (breathe in air), solubility in water (drink water), and octanol-water partitions (accumulation in fat). 

Another example is polychlorinated biphenyls (PCBs), which have 10 hydrogen atoms that can be substituted by chlorine atoms. There are three types of site the four a sites near the bridge between the two phenyl fragments, the four p sites farther... 

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