四メチル化合物におけるC-13,Si-29及びSn-119 NMR化学シフトに対する塩素及び臭素原子による置換基効果

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Carbon-13,silicon-29 and tin-119 chemical shifts were measured for chloro and bromosubstituted compounds [(CH_3)_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 ^<13>C, ^<29>Si and ^<119>Sn chemical shifts of monochloro-substituted compounds were shifted to a lower field by 30〜172 ppm in the order of ^<29>Si, ^<13>C and ^<119>Sn, which could be explained by an inductive effect. The ^<13>C chemical shifts for chloro-substituted compounds were shifted to a lower field in order of mono, di, tri and tetrachloro substituents, however, the ^<119>Sn 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 ^<13>C, ^<29>Si and ^<119>Sn chemical shifts of monobromo-substituted compounds were also shifted to a lower field by 27〜135 ppm in the same order as that of monochloro-substituted compounds. The ^<13>C, ^<29>Si and ^<119>Sn 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.
1997-11-05