NMR Spectroscopy
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What are the 2 types of spectroscopy
13C NMR 1H (proton) NMR
How are peaks determined in 13C?
Number of different C environments
How many 13C signals (peaks) would there be in propanal?
3
How many 13C signals (peaks) would there be in 2-chloro,2-methylpropane?
2
How many 13C signals (peaks) would there be in 1-methyl-4-nitrobenzene?
5
How are peaks determined in 1H?
Number of different H environments
How are ratios determined in H1
Number of H atoms on the neighbouring C atom
How many 1H signals (peaks) and ratio would there be in 2-bromobutane?
4 3:1:2:3
How many 1H signals (peaks) and ratio would there be in propene?
3 3:1:2
Solvents used in NMR and why?
CCl4 - Inert, non polar for non polar molecules CDCl3 - Inert, polar for polar molecules
What is TMS?
Tetramethylsilane to calibrate the spectrum
TMS properties
Gives one signal Signal does not merge with other signals Non-toxic Inert Low boiling point so easily removed
How is splitting of peaks in 1H NMR decided
Number of inequivalent H’s on neighbouring C atoms + 1
Peak of 1H NMR connected to an O or N molecule
Singlet peak
State why Si(CH3)4, CCl4 and CDCl3 are used in 1H NMR spectroscopy. Explain how their properties make them suitable for use in 1H NMR spectroscopy. [6]
Stage 1 [1+2] CDCl3 / CCl4 as solvent TMS as reference / calibration Inert Stage 2 [3+4] CDCl3 / CCl4 both have no H atoms CCl4 non polar CDCl3 polar covalent molecule Stage 3 [5+6] Gives one signal Signal in an area away from other typical H signals Low bp / easy to remove
What does integration value represent
Number of H atom in each environment
What does splitting value represent
Number of H atoms in adajcent in environment - 1