32 structure determination
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what is NMR spectroscopy used for?
to determine structures of unknown organic substances
why is NMR a powerful technique?
• it is easy to obtain a spectrum • only a small amount of sample needed • non-destructive
why is carbon-13 used for NMR?
odd number of nucleons needed for a residual spin
what are two things you need to be able to interpret in a carbon-13 NMR?
• number of peaks tells you number of C environments • location of peaks tells you the type of C environment
what is used as a reference standard for chemical shifts?
tetra methyl silane (TMS)
what is the structure of TMS?
silicon surrounded by 4 methyl groups
why is TMS used as a standard?
• generates one sharp peak • unreactive • highly volatile • peak always found on far right of spectrum
why is it good that TMS is unreactive?
so it won’t affect the sample being tested
why is it good that TMS is highly volatile?
it can be removed from the sample after the analysis