A simple numerical code for polychlorinated compound classes allowing an unequivocal derivation of the steric structure I: Polychlorinated biphenyls and bornanes

A structure related numbering system is proposed for classes of polychlorinated compounds with a large number of congeners. The number of a congener can be decoded in a simple way to obtain its precise structure. The application of the system to polychlorinated biphenyls and bornanes is described. First, a binary code number is created as follows. For each single PCB ring, each position with a Cl-substitution is marked by the figure 1 and no substitution by 0. For example, the binary code of CB 105, 2,3,3′,4,4′-PeCB, is for ring A 11100 (2,3,4 of the positions 2,3,4,5,6 are CI-substituted) and of ring B 01100 (3′,4′). These binary numbers are converted into decimal numbers as usual by adding the corresponding powers of 2. This gives for ring A 1+2+4+0+0=7 and for ring B 0+2+4+0+0=6. The final numerical code is combined with a hyphen resulting in 7-6 for CB 105. It can be converted into the precise steric structure by using the inverse approach. A further advantage of this system is a direct information about the degree of ortho-substitution from the numerical codes. The codes for polychlorinated bornanes are divided into a ring code and a code for the methyl groups. The latter allows an unequivocal identification of the steric positions of the CI-atoms at the methyl groups. Furthermore, congeners with identical ring substitution will have the same ring code.