Spectrum of the Month
April 2000
Silicon NMR Studies and Conditions
Dima (Dimitry Yandulov) took some silicon-29 spectra on our I400 spectrometer. He measured the following compound
As external reference, he used 50% TMS in his solvent (50% benzene). This allowed him to determine the scale approximately. He added some TMS to his sample to also have an internal reference. His observation was that this procedure was necessary to exactly set the scale.
To identify his peaks he took spectra under different proton decoupling conditions:
dm='n' : no decoupling
dm='nny': decoupling during the detection
dm='yyy' decoupling during the detection and NOE transfer during the relaxation period.
Notice the effect of the NOE transfer to the signals: Silicon has a negative spin quantum number. The different mobility of his groups and the small TMS give rise to positive and negative NOE transfers. The intensities of the spectra are therefore not very informative. The nicely resolved multiplet structure without decoupling allowed him to identify his groups with his peaks.
Since many of you have silicon in their samples, sometimes as part of protecting groups, his experiences may be of interest to you. His most important message is: use as much sample as you can. As external reference, he used 50% TMS in his solvent (50% benzene) and got signal in 16 scans. For his sample he used about 10% by volume and took about 2.5 hours.
Thank you, Dima
