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Interpreting
and explaining the
H-1 (proton) NMR spectrum of methyl 2-hydroxybenzoate
(methyl salicylate)
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Dr Phil Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK A level chemistry courses,
IB chemistry & US K12 grade
11, grade 12 and AP honors chemistry courses: Molecular
spectroscopy - analysing the 1H NMR spectra of
methyl 2-hydroxybenzoate,
methyl salicylate
[spectra
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1H NMR spectrum of
methyl 2-hydroxybenzoate,
methyl
salicylate
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H-1 proton NMR spectroscopy -
spectra index
Introductory note on the 1H NMR spectra of methyl 2-hydroxybenzoate
(methyl salicylate)
Students and teachers please note my explanation of the
proton NMR spectrum of methyl 2-hydroxybenzoate (methyl
salicylate) is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
methyl 2-hydroxybenzoate (methyl salicylate) are
confined to a proton spin-spin
coupling effects analysed using the n+1 rule for adjacent
non-equivalent proton fields (n is the number of neighbouring
protons in a non-equivalent different chemical environment for the
methyl 2-hydroxybenzoate (methyl salicylate) molecule).
It is assumed that the integrated intensities of the
δ
chemical shifts give the ratio of the protons in the different
non-equivalent chemical environments of the methyl
2-hydroxybenzoate (methyl salicylate) molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like methyl 2-hydroxybenzoate (methyl
salicylate), is CDCl3 and other
deuterated solvents to avoid confusion with a 1H NMR
signal, 2D (2H) has a different chemical
shift.
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 resonances, called chemical shifts, are measured
with respect to the TMS, and depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - methyl 2-hydroxybenzoate here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of methyl 2-hydroxybenzoate 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 methyl 2-hydroxybenzoate molecule.
C8H8O3,
or
 ,
methyl 2-hydroxybenzoate (methyl salicylate, 'oil of wintergreen'
For more see
The molecular structure and naming of
carboxylic acids and derivatives
For more see
The molecular structure
and naming of aromatic compounds
Interpreting the
H-1 NMR spectrum of
methyl 2-hydroxybenzoate
For relatively simple molecules, the low
resolution H-1 NMR spectrum of methyl 2-hydroxybenzoate is a good starting point
(low resolution diagram above).
The 8 hydrogen atoms (protons) of methyl
2-hydroxybenzoate occupy
6
different chemical environments so that the low resolution NMR
spectra should show 6 principal
1H resonance peaks of different H-1 NMR chemical shifts (diagram above for
methyl 2-hydroxybenzoate).
Note the lack of symmetry results in 6 different 1H chemical
shifts for this molecule.
Note the proton ratio 3:1:1:1:1:1 of the
8 protons of methyl 2-hydroxybenzoate
in the 6 chemically different proton environments
Chemical shifts (a) to (f) on the H-1 NMR
spectrum diagram for methyl 2-hydroxybenzoate.
Although there are 8 hydrogen atoms in the molecule, the
proton NMR spectrum shows there are only 6 possible different chemical
environments for the hydrogen atoms in methyl 2-hydroxybenzoate molecule.
The integrated proton signal ratio of
3:1:1:1:1:1 observed
in the high resolution H-1 NMR spectrum, corresponds with
the structural formula of methyl 2-hydroxybenzoate.
The high resolution 1H NMR spectrum of methyl 2-hydroxybenzoate
(methyl salicylate)
In terms of spin-spin coupling from the possible proton magnetic orientations,
for methyl 2-hydroxybenzoate I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
The high resolution spectra of methyl
2-hydroxybenzoate
shows 6 groups of proton resonances and in the ratio expected from the
structural
formula of methyl 2-hydroxybenzoate, but we can now consider the splitting of
resonance lines from the spin-spin coupling in the molecule of
methyl 2-hydroxybenzoate.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of methyl 2-hydroxybenzoate - since the peak' is at the apex of a band of
H-1 NMR resonances due to spin - spin coupling field splitting effects - see high resolution
notes on methyl 2-hydroxybenzoate below.
So, using the chemical shifts and applying the
n+1 rule to
methyl 2-hydroxybenzoate
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
1H NMR resonance
(a) 1H
Chemical shift δ 3.93 ppm:
A singlet resonance for the methyl protons, since no
protons on an adjacent carbon atom.
1H NMR resonance
(b) 1H
Chemical shift δ 10.74 ppm:
A singlet for the hydroxyl proton, since no protons on
an adjacent carbon atom.
This hydroxyl proton of
the phenol group can be distinguished from other protons in the methyl
2-hydroxybenzoate molecule by the addition of D2O to the CDCl3
(or other) solvent, and the ensuing rapid proton exchange reduces the
1H NMR shift signal, which is different to the 2D
(2H) chemical shift.
1H NMR resonance
(c) 1H
Chemical shift δ 6.97 ppm:
The ring carbon 3 proton resonance is split into a
doublet by the ring carbon 4 proton (n+1 = 2). The split (c) resonance
overlap with the split (e) resonances.
A series of singlets and doublets in the region of δ 6.4
and 8.2 ppm is indicative of benzene ring protons - you can see this in 1H
NMR resonances (c) to (f) in the spectrum of methyl 2-hydroxybenzoate.
1H NMR resonance
(d) 1H
Chemical shift δ 7.43 ppm:
The ring carbon 4 proton resonance is split into a
triplet by the ring carbon protons 3 and 5 (n+2 = 3).
1H NMR resonance
(e) 1H
Chemical shift δ 6.87 ppm:
The ring carbon 5 proton resonance is split into a
triplet by the ring carbon protons 4 and 6 (n+2 = 3).
1H NMR resonance
(f) 1H
Chemical shift δ
7.81 ppm:
The ring carbon 6 proton resonance is split into a
doublet by the ring carbon 5 proton (n+1 = 2).
The splitting pattern from proton
spin-spin coupling effects is analysed using the n+1 rule for
adjacent non-equivalent proton fields (n is the number of
neighbouring protons in a non-equivalent different chemical
environment) and applied to the 1H NMR spectrum of methyl
2-hydroxybenzoate (methyl salicylate).
|
Number of directly adjacent protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule on spin-spin coupling and the theoretical ratio of line intensities |
|
0
means no splitting |
|
|
|
|
|
|
1 |
|
|
|
|
|
|
|
1
creates a doublet |
|
|
|
|
|
1 |
|
1 |
|
|
|
|
|
|
2
creates a triplet |
|
|
|
|
1 |
|
2 |
|
1 |
|
|
|
|
|
3
creates a quartet |
|
|
|
1 |
|
3 |
|
3 |
|
1 |
|
|
|
|
4
creates a quintet |
|
|
1 |
|
4 |
|
6 |
|
4 |
|
1 |
|
|
|
5
creates a sextet |
|
1 |
|
5 |
|
10 |
|
10 |
|
5 |
|
1 |
|
|
6
creates a septet |
1 |
|
6 |
|
15 |
|
20 |
|
15 |
|
6 |
|
1 |
Key words & phrases:
isomer
of molecular formula C8H8O3 Interpreting the proton H-1 NMR spectra of methyl 2-hydroxybenzoate, low resolution & high
resolution proton nmr spectra of methyl 2-hydroxybenzoate, H-1 nmr spectrum of
methyl 2-hydroxybenzoate, understanding the
hydrogen-1 nmr spectrum of methyl 2-hydroxybenzoate, explaining the line splitting patterns from
spin-spin coupling in the high resolution H-1 nmr spectra of methyl
2-hydroxybenzoate, revising
the H-1 nmr spectrum of methyl 2-hydroxybenzoate, proton nmr of methyl
2-hydroxybenzoate, ppm chemical shifts of the H-1
nmr spectrum of methyl 2-hydroxybenzoate, explaining and analyzing spin spin line splitting in the
H-1 nmr spectrum, how to construct the diagram of the 1H nmr spectrum of methyl
2-hydroxybenzoate, how to work out the
number of chemically different protons in the structure of the methyl
2-hydroxybenzoate organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of methyl 2-hydroxybenzoate using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of methyl 2-hydroxybenzoate deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of methyl 2-hydroxybenzoate
examining the 1H nmr spectrum of methyl 2-hydroxybenzoate analysing the 1H nmr spectrum of
methyl 2-hydroxybenzoate
how do you sketch and interpret the H-1 NMR spectrum of methyl 2-hydroxybenzoate
interpreting interpretation of the 1H proton spin-spin coupling causing line
splitting in the NMR spectrum of methyl 2-hydroxybenzoate
assignment of chemical shifts in the
proton 1H NMR spectrum of methyl 2-hydroxybenzoate formula explaining spin-spin
coupling for line splitting for
methyl salicylate old names
ester phenol functional group
How do you interpret the H-1 NMR spectrum of
methyl 2-hydroxybenzoate (methyl salicylate) How to interpret
the H-1 NMR spectrum of methyl 2-hydroxybenzoate (methyl salicylate) Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the methyl
2-hydroxybenzoate (methyl salicylate)
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of methyl 2-hydroxybenzoate (methyl salicylate). How to explain the H-1 NMR spectrum of
methyl 2-hydroxybenzoate (methyl salicylate). The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the methyl 2-hydroxybenzoate (methyl salicylate) molecule. How to work out the molecular
structure of the methyl 2-hydroxybenzoate (methyl salicylate) molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the methyl
2-hydroxybenzoate (methyl salicylate)
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the methyl 2-hydroxybenzoate (methyl
salicylate)
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of methyl 2-hydroxybenzoate (methyl salicylate). interpretation
diagram explaining the proton splitting pattern produced from the
n+1 rule and the theoretical ratio of chemical shift
δ and values of
intensities for the proton NMR spectrum lines of methyl 2-hydroxybenzoate
(methyl salicylate)
Links associated
with
methyl 2-hydroxybenzoate
The infrared spectrum of methyl
2-hydroxybenzoate (methyl salicylate)
The mass
spectrum of methyl 2-hydroxybenzoate (methyl
salicylate)
The C-13 NMR spectrum of
methyl 2-hydroxybenzoate (methyl salicylate)
INDEX of all revision notes on
CARBOXYLIC ACIDS and DERIVATIVES
INDEX of all AROMATIC COMPOUND chemistry
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H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
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spectroscopy (1H NMR spectra of methyl 2-hydroxybenzoate,
methyl salicylate) are
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