but what are modern NMR machines are sensitive enough to give
a full spectra for C13
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what is the The C13 spectra is a simpler spectrum than
the H NMR
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In a C13 NMR spectrum, what is there one signal (peak) for
each set of equivalent C atoms.
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In an H NMR spectrum, what is there one signal for each
set of equivalent H atoms.
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In addition what is the intensity (integration value) of each signal is proportional to
the number of equivalent H atoms it represents.
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What are Samples are dissolved in
solvents without any 1H atoms, e.g. CCl4, CDCl3.
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What does This means
that in the H NMR the solvent will not give any peaks
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What solvent is used in c13 NMR
The same solvent is used in C13 NMR and in this case there will be one peak due to the solvent that will appear on the spectrum.
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However, what is known
where this peak is so it can be ignored.
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What is A small amount of added to the sample to calibrate the spectrum
TMS (tetramethylsilane)
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What is The same calibration compound is used for
both H and C NMR
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Why is TMS is used
because: •its signal is away from all the others •it only gives one signal •it is non-toxic •it is inert •it has a low boiling point and so can be removed from sample easily
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What is the The spectra are recorded on
a scale known as the chemical shift (δ), which is how much the field has shifted away from the field for TMS..
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How is TMS arranged
Si with 4 methyl groups
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what is The δ is a measure in parts per million (ppm)
is a relative scale of how far the frequency of the proton signal has shifted away from that for TMS.
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What does the The δ depends on
what other atoms/groups are near the H –
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more electronegative groups gives a
greater shift.
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In high resolution H NMR what can each signal in the spectrum be split into
further lines due to inequivalent H’s on neighbouring C atoms.
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What do Nuclei in identical chemical environments do not show
coupling amongst themselves!
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Splitting of peak =
number of inequivalent H’s on neighbouring C atoms + 1
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signal, Split number of peaks, number of neighbouring inequivalent H atoms and relative size of Singlet
1,0, N/A
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signal, Split number of peaks, number of neighbouring inequivalent H atoms and relative size of doublet
2,1,1:1
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signal, Split number of peaks, number of neighbouring inequivalent H atoms and relative size of triplet
3,2,1:2:1
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signal, Split number of peaks, number of neighbouring inequivalent H atoms and relative size of quartet
4,3,1:3:3:1
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what do Hydrogens bonded to a Nitrogen or Oxygen usually do not couple with
other protons and appear as singlets on the NMR spectra
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Other cards in this set
Card 2
Front
What is There is only around 1% of C13 in
Back
organic molecules
Card 3
Front
but what are modern NMR machines are sensitive enough to give
Back
Card 4
Front
what is the The C13 spectra is a simpler spectrum than
Back
Card 5
Front
In a C13 NMR spectrum, what is there one signal (peak) for
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