C-13 CHEMICAL-SHIFTS FOR 70 HALOMETHANES

Somayajulu and Zwolinski have recently shown that nonbonded interactions between trios of adjacent bonds play an important part in the correlation of the carbon-13 chemical shifts of halomethanes and developed a procedure known as the trigonal additivity procedure. This procedure is an improvement over the geminal additivity procedure which is based on contributions from bonds and pairs of bonds. For the 70 halomethanes we require 15 geminal parameters and 35 trigonal parameters. The available carbon-13 chemical shifts permit the determination of all 15 geminal parameters while only 25 of the 35 trigonal parameters could be determined. A proposed procedure allows one to calculate the missing 10 trigonal parameters and thereby the chemical shifts of all 70 halomethanes. Carbon-13 chemical shifts determined by experiment for 8 halomethanes are reported. © 1979.