Substituent effect by chlorine and bromine atoms for carbon-13, silicon-29 and tin-119 NMR chemical shifts in tetramethyl compounds.

Abstract

Carbon-13, silicon-29 and tin-119 chemical shifts were measured for chloro and bromo-substituted compounds [(CH3)nMX4-n; M=C, Si, Sn;n=0-4], and the behavior of the chemical shifts for carbon, silicon and tin atoms in those compounds were investigated. The 13C, 29Si and 119Sn chemical shifts of monochloro-substituted compounds were shifted to a lower field by 30-172 ppm in the order of 29Si, 13C and 119Sn, which could. be explained by an inductive effect. The 13C chemical shifts for chloro-substituted compounds were shifted to a lower field in order of mono, di, tri and tetrachloro substituents, however, the 119Sn chemical shifts in those compounds were shifted to higher fields with increasing number of chlorine atoms in a molecule. This is considered to be due to the effect of a steric compression between the substituted chlorine atoms. The 13C, 29Si and 119Sn chemical shifts of monobromo-substituted compounds were also shifted to a lower field by 27135 ppm in the same order as that of monochloro-substituted compounds. The 13C, 29Si and 119Sn chemical shifts for bromo-substituted compounds shifted largely toward a higher field with increasing number of bromine atoms in a molecule, which probably could be attributed to the heavy atom effect.