Topic 19 - Modern Analytical Techniques 2
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What is high resolution mass spectrometry?
mass spectrometry which can measure Mr to 4 decimal places (more accurate)
What can high resolution mass spectrometry be used for?
to distinguish between compounds that appear to have same Mr when rounded to a whole number
What does NMR stand for?
nuclear magnetic resonance
What is NMR (nuclear magnetic resonance)?
an analytical technique which uses a magnetic field to align protons in the nucleus of hydrogen atoms and carbon-13 atoms -is used to determine structure of a compound
What is used as a standard in NMR?
tetramethylsilane (TMS) (CH3)4Si
Why is TMS used as a standard/comparative peak in NMR?
• all 12 of its hydrogen atoms are in the same environment (no splitting pattern) • all of its hydrogen atoms are more heavily shielded in any other molecule (aka their e- lie closer to the hydrogens than in any other molecule) • it is inert • its peak is to the right so doesn’t overlap with other peaks • it has a low boiling temperature/is volatile so can be easily removed • gives a strong signal so only a small amount needed
What does C-13 NMR provide information about?
position of C-13 atoms in a molecule
What does proton NMR provide information about?
positions of H atoms in a molecle
What does low resolution NMR tell us?
• number of hydrogen environments - number of hydrogen atoms in each hydrogen environment
What does high resolution NMR tell us?
• number of hydrogen environments • number of hydrogen atoms in each hydrogen environment • how many hydrogens are on adjacent carbon
What is the number of peaks on a NMR spectra equivalent to?
number of hydrogen environments
What is the height of a peak on a low resolution NMR spectra equivalent to?
how many hydrogen atoms are in that environment
What is the splitting pattern on a high resolution NMR spectra equivalent to?
the number of hydrogen atoms are on the adjacent carbon plus one (N+1 rule)
What is the area under a cluster on a high resolution NMR spectra equivalent to?
number of hydrogen atoms in environment
How many hydrogens are on the adjacent carbon to a singlet?
0
How many hydrogens are on the adjacent carbon to a doublet?
1
How many hydrogens are on the adjacent carbon to a triplet?
2
How many hydrogens are on the adjacent carbon to a quartet?
3
How many hydrogens are on the adjacent carbon to a quintet?
4
What do you call the splitting pattern when there are 0 carbons on the adjacent carbon?
singlet
What do you call the splitting pattern when there is 1 carbon on the adjacent carbon?
doublet
What do you call the splitting pattern when there are 2 carbons on the adjacent carbon?
triplet
What do you call the splitting pattern when there are 3 carbons on the adjacent carbon?
quartet
What is the N+1 rule?
the number of subpeaks within a cluster on a high resolution NMR is equivalent to the umber of hydrogen atoms on the adjacent carbon plus one