M6 Spectroscopy Q&A
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What information about a molecule can be deduced from a 1H NMR spectrum?
• The number of peaks gives the number of proton environments in the molecule • The relative areas (intensities) of the peaks gives the number of protons in each environment • The chemical shift value gives the type of proton environment, e.g. d 1-2 ppm R-CH • The splitting pattern gives the number of protons on the adjacent carbon; the ‘n + 1’ rule: if there are n protons on the adjacent carbon, the peak is split into n+1 peaks • e.g. if there are 2 protons on the adjacent carbon, the peak is split into a triplet
Describe the use of TMS in NMR spectroscopy
• It is a standard – chemical shift d set as zero • Give large singlet peak at higher frequency than other organic compounds • Also chemically inert (does not react with sample) and volatile (can be removed from sample)
Describe the use of deuterated solvents, e.g D2O in 1H NMR spectroscopy
• Solvents dissolve the sample • In 1H NMR hydrogen atoms present in a solvent would give peaks on spectrum • All hydrogen atoms are replaced by 2H, deuterium, which does not give peaks • If a sample is mixed with the deuterated solvent D2O (only), labile protons on O-H and N-H groups are replaced by deuterium and O-H and N-H peaks disappear from the sample • This is useful to confirm the presence of O-H and N-H groups