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Unformatted text preview: The Standard for Chemical Shift Tetramethylsilane ( TMS ), (CH 3 ) 4 Si, is a chemically inert compound with 12 equivalent H. This single resonance appears at a higher field than most hydrocarbons and other organic compounds. Resonances are reported in frequency units relative to the single resonance in TMS regardless of how the nmr experiment is actually carried out (variable B o or variable rf). Example: A resonance in compound A B E TMS A ! TMS ! A !" = " A " TMS- spectral display A "low field" "high field" TMS chemical shift of A reported in frequency units !" = " A " TMS- The Delta ( ! ) Unit for Chemical Shift Most proton resonances are within hundreds of Hz "downfield" from the TMS resonance. The chemical shift in frequency units depends on the type of nmr spectrometer used in the experiment, as discussed below. Chemical shifts are reported in the ! unit which is independent of the instrument used....
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- Summer '07
- Organic chemistry