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The H-1
hydrogen-1 (proton) NMR spectrum of ethanoic acid
(acetic acid)
Doc Brown's
Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB
KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry
courses involving molecular spectroscopy analysing H-1 NMR spectra of
ethanoic acid
See also
comparing the infrared, mass, 1H and 13C NMR spectra of
the isomers of C2H4O2
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose protons are arbitrarily given a chemical shift of 0.0 ppm.
This is the 'standard' in 1H NMR spectroscopy and all
other proton shifts, called chemical shifts, depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - ethanoic acid here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of ethanoic acid represent the peaks of the intensity of
the chemical shifts of (which are often groups of split lines at
high resolution) AND the relative integrated areas under the peaks
gives you the ratio of protons in the different chemical
environments of the ethanoic acid molecule.
Ethanoic acid,
C2H4O2,
 ,
 ,
 ,
For more see
Structure and naming of CARBOXYLIC ACIDS and DERIVATIVES,
including isomers
Interpreting the
H-1 NMR spectrum of ethanoic acid
For relatively simple molecules, the low
resolution H-1 NMR spectrum of ethanoic acid is a good starting point.
The hydrogen atoms (protons) of ethanoic acid occupy
2 different
chemical environments so that the H-1 proton low resolution NMR
spectra should show principal 2 peaks in the ratio 3 : 1 (diagram above).
CH3COOH
(note the 3: 1 ratio of the 2 colours of the protons indicating
the 2 chemically different environments)
The integrated proton ratio observed of 3:1, corresponds with
the structural formula of ethanoic acid.
The two 1H chemical environments in
the ethanoic acid molecule are the methyl group protons (CH3,
2.1 ppm chemical shift) and the hydroxy proton (OH, 11.4 ppm
chemical shift).
The latter is quite large due to the
combined field effect of the two highly electronegative
oxygen atoms.
There is no need to consider the very high resolution spectrum of ethanoic acid,
as
there are no other immediate protons adjacent to the H of the
hydroxyl OH group, or
the H's of the CH3 group so the spin-spin splitting
lines would be to
weak to be observed.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 2 isomers of C2H4O2
NOTE: The images are linked to their
original detailed spectral analysis pages AND can be doubled in
size with touch screens to
increase the definition to the original ethanoic acid (acetic
acid) and
methyl methanoate (methyl formate) image sizes. |
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INFRARED SPECTRA:
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, the most striking
difference is the broad O-H stretching band ~3200 cm-1,
found in the infrared spectrum of carboxylic acids, but absent in
the infrared spectrum of esters. |
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MASS SPECTRA: Apart
from the m/z of 60 for the parent molecular ion and m/z 15 ion [CH3]+,
both ethanoic acid and methyl methanoate show few similarities in their mass
spectra. Their base ion peaks are quite different - for ethanoic
acid it is m/z 43 and for methyl methanoate it is m/z 31. |
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1H NMR SPECTRA: The 1H NMR spectra of
ethanoic acid and methyl methanoate are similar with two
'wide-apart' chemical shift singlet peaks in the
integrated proton ratio of 3:1 (meaning 2 different
1H chemical environments). However, although no
splitting is observed, the 1H chemical shifts for the
two molecules are different, those of ethanoic acid are much
further apart. |
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13C NMR SPECTRA: The 13C NMR spectra of
ethanoic acid and methyl methanoate are similar, both molecules give two
C-13 NMR spectral lines (meaning 2
different 13C chemical environments). |
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Number of protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule and the theoretical ratio of line intensities |
| 0
means no splitting |
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1 |
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| 1
creates a doublet |
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1 |
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1 |
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| 2
creates a triplet |
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1 |
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2 |
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1 |
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| 3
creates a quartet |
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1 |
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3 |
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3 |
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1 |
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| 4
creates a quintet |
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1 |
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4 |
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6 |
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4 |
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1 |
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| 5
creates a sextet |
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1 |
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5 |
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10 |
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10 |
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5 |
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1 |
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| 6
creates a septet |
1 |
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6 |
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15 |
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20 |
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15 |
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6 |
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1 |
Key words & phrases: Interpreting the proton H-1 NMR spectra of ethanoic
acid, low resolution & high resolution proton
nmr spectra of ethanoic acid, H-1 nmr spectrum of ethanoic acid, understanding the
hydrogen-1 nmr spectrum of ethanoic acid, explaining the line splitting patterns in the
high resolution H-1 nmr spectra of ethanoic acid, revising the H-1 nmr spectrum of
ethanoic acid,
proton nmr of ethanoic acid, ppm chemical shifts of the H-1 nmr spectrum of
ethanoic acid,
explaining and analyzing spin spin line splitting in the H-1 nmr spectrum, how
to construct the diagram of the H-1 nmr spectrum of ethanoic acid, how to work out the
number of chemically different protons in the structure of the ethanoic acid
organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1
proton NMR spectrum of ethanoic acid
Molecular structure diagram of the
proton NMR diagram for the 1H NMR spectrum of ethanoic acid. The proton ratio in the
1H NMR spectrum of ethanoic acid. Deducing the number of different chemical
environments of the protons in the ethanoic acid molecule from the 1H chemical shifts
in the hydrogen-1 NMR spectrum of ethanoic acid. Analysing the high resolution 1H NMR
spectrum of ethanoic acid. Analysing the low resolution 1H NMR spectrum of
ethanoic acid. You
may need to know the relative molecular mass of ethanoic acid to deduce the molecular
formula from the proton ratio of the 1H NMR spectrum of ethanoic acid. Revision notes
on the proton NMR spectrum of ethanoic acid. Matching and deducing the structure of
the ethanoic acid molecule from its hydrogen-1 NMR spectrum.
Proton NMR spectroscopy of carboxylic acids, 1H NMR spectra of ethanoic
acid, an isomer of molecular formula C2H4O2
Associated links
The chemistry of CARBOXYLIC ACIDS and DERIVATIVES
revision notes INDEX
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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