The proton NMR signal of TMS is a singlet at 0 ppm ..... right? - WRONG!Naturally occurring TMS is a mixture of isotopomers. Silicon is 92.2% silicon -28 (I = 0), 4.7% silicon-29 (I = 1/2) and 3.1 silicon-30 (I = 0). Carbon is 98.9% carbon-12 (I = 0) and 1.1% carbon-13 (I = 1/2). Each isotopomer has a different NMR spectrum. The protons are coupled to both 13C and 29Si but not 12C and 28Si.The figure below shows a 400 MHz proton NMR spectrum of TMS. The major isotopomers responsible for the lines are labelled.