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Interpreting the
H-1 hydrogen-1 (proton) NMR spectrum of 1,3-dioxane
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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 1,3-dioxane
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 - 1,3-dioxane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 1,3-dioxane 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 1,3-dioxane molecule.
Interpreting the
H-1 NMR spectrum of
1,3-dioxane
In terms of spin-spin coupling from the possible proton magnetic orientations,
for 1,3-dioxane I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. -CH2-CH2-,
protons.
For relatively simple molecules, the low
resolution H-1 NMR spectrum of 1,3-dioxane is a good starting point
(low resolution diagram above).
The hydrogen atoms (protons) of 1,3-dioxane occupy
3
different chemical environments so that the low resolution NMR
spectra should show 3 principal peaks of different H-1 NMR chemical shifts
in the ratio of 2:4:2, observed as an integrated proton
ratio of 1:2:1 (diagram above for
1,3-dioxane).
Chemical shifts (a) to (c) on the H-1 NMR
spectrum diagram for 1,3-dioxane.
Although there are 8 hydrogen atoms in the molecule,
there are only 3 possible different chemical
environments for the hydrogen atoms in 1,3-dioxane molecule.
The integrated signal proton ratio 1:2:1 observed
in the high resolution H-1 NMR spectrum, corresponds with
the structural formula of 1,3-dioxane.
The high resolution 1H NMR
spectrum of 1,3-dioxane
The high resolution spectra of 1,3-dioxane
shows 3 groups of proton resonances and in the 1:2:1 ratio expected from the
structural
formula of 1,3-dioxane.
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of 1,3-dioxane - 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 1,3-dioxane below.
So, using the chemical shifts and applying the
n+1 rule to
1,3-dioxane
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
(a) 1H
Chemical shift 1.78 ppm, CH2 protons furthest from the oxygen
atoms
This resonance is split into a 1:4:6:4:1
quintet by the adjacent CH2 protons on either
side (n+1 = 5).
Evidence for the presence of a CH2-CHx-CH2 grouping
in the molecule of 1,3-dioxane
(b) 1H
Chemical shift 3.91 ppm, 2 x CH2 protons nearest on either
side of the oxygen atoms
This resonance is split by the adjacent
CH2 protons into a 1:2:1 triplet (n+1 = 3)
Evidence for the presence of a 2nd CH2 group
in the molecule of 1,3-dioxane
(c) 1H
Chemical shift 4.85 ppm, CH2 protons between the oxygen
atoms.
This resonance is not split because
there are no protons on an adjacent atom, these protons
are 'isolated' between the oxygen atoms.
From the proto ratio and molecular
formula, gives evidence for the presence of a 3rd group
of CH2 protons in the molecule of 1,3-dioxane
|
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:
C4H8O2
Interpreting the proton H-1 NMR spectra of 1,3-dioxane, low resolution & high resolution proton
nmr spectra of 1,3-dioxane, H-1 nmr spectrum of 1,3-dioxane, understanding the
hydrogen-1 nmr spectrum of 1,3-dioxane, explaining the line splitting patterns from
spin-spin coupling in the
high resolution H-1 nmr spectra of 1,3-dioxane, revising the H-1 nmr spectrum of
1,3-dioxane,
proton nmr of 1,3-dioxane, ppm chemical shifts of the H-1 nmr spectrum of
1,3-dioxane,
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 1,3-dioxane, how to work out the
number of chemically different protons in the structure of the 1,3-dioxane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 1,3-dioxane using the n+1 rule to explain the spin - spin coupling ine
splitting in the proton nmr spectrum of 1,3-dioxane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 1,3-dioxane
examining the 1H nmr spectrum of 1,3-dioxane analysing the 1-H nmr spectrum of
1,3-dioxane
how do you sketch and interpret the H-1 NMR spectrum of 1,3-dioxane interpreting
interpretation of the 1H proton spin-spin coupling causing line splitting in the
NMR spectrum of 1,3-dioxane
assignment of chemical shifts in the
proton 1H NMR spectrum of 1,3-dioxane formula explaining spin-spin coupling for
line splitting for 1,3-dioxane meta-dioxane m-dioxane
ether functional group
Links associated
with 1,3-dioxane
H-1 proton NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
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Chemistry Notes
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