In carbon-13 NMR, what do the
number of peaks represent?
The number of chemically
different carbon atoms present
What are the two main factors
to look for in the analysis of
carbon-13 NMR spectra?
The number of peaks present &
the chemical shift of the peak
Which two features are
present in proton NMR spectra,
but not in carbon-13 NMR
spectra?
The relative peak area
(integration value) and the
splitting of the peak
What does the splitting of the
proton NMR peak tell you?
The number of protons on the
carbon (or other) atom adjacent
to a particular type of proton
Which solvent is used in proton
NMR?
TMS (Tetramethylsilane)
What does the area under the
peak represent in proton NMR?
The number of protons
responsible for the peak
What splitting pattern will be
shown by a group adjacent to a
methyl (CH3) group?
A quartet
Combined spectral analysis
Aim
• Use mass spectrometry, Infra-red
and NMR spectra to deduce the
structure of a compound.
Combined spectral analysis
A compound containing 58.8% carbon, 9.8% hydrogen and 31.4% oxygen is subjected to
mass spectrometry and found to give intense peaks at m/z = 43 and m/z = 71, in
addition to a molecular ion peak at m/z = 102.
Infra-red analysis of the molecule showed a sharp peak at m/z = 1710 cm-1.
A proton nmr spectrum of the molecule yielded the following peaks:
Chemical shift
Splitting
Integration
factor
0.8
Triplet
3
1.1
Sextet
2
2.3
Triplet
2
3.7
Singlet
3
Deduce the structure of the molecule and account for the formation of all the peaks
the spectra.
Answer
• Molecular formula = C5H10O2
• mass spectrum:
peak at 43 from: CH3CH2CH2COOCH3+.  CH3CH2CH2+ + .COOCH3
peak at 71 from: CH3CH2CH2COOCH3+.  CH3CH2CH2CO+ + .OCH3
• infra-red spectrum:
peak at 1710 cm-1 indicates a carbonyl
•
•
•
•
•
proton nmr spectrum:
peak at 0.8 is CH3- adjacent to -CH2peak at 1.1 is -CH2- adjacent to CH3- and -CH2peak at 2.3 is -CH2CO- adjacent to -CH2peak at 3.7 is CH3O-
• so molecule is methyl butanoate, CH3CH2CH2COOCH3
Past exam questions