Skeletal and chlorine effects on C-13-NMR chemical shifts of chlorinated polycyclic systems

In order to establish a comparative analysis of chemical shifts caused by r ing compression effects or by the presence of a chlorine atom on strained c hlorinated carbons, a series of the chlorinated and dechlorinated polycycli c structures derived from "aldrin" (5) and "isodrin" (14) was studied. Comp ounds were classified in four different groups, according to their conforma tion and number of ring such as: endo-exo and endo-endo tetracyclics, penta cyclics and hexacyclics. The C-13 chemical shift comparison between the chl orinated and dechlorinated compounds showed that when C-9 and C-10 are olef inic carbons, it occurs a shielding of 0.5-2.4 ppm for endo-endo tetracycli cs and of 4.7-7.6 ppm for endo-exo tetracyclic. The chemical shift variatio n for C-11 reaches 49-53 ppm for endo-exo and endo-endo tetracyclics, 54 pp m for pentacyclic and 56-59 ppm for hexacyclic compounds. From these data, it was possible to observe the influence of ring compression on the chemica l shifts.