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)_nMX_4-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.