1H Proton Nmr Spectrum Of 1,2-dioxane C4H8O2 Low/high Resolution ...

Interpreting and explaining the H-1 hydrogen-1 (proton) NMR spectrum of 1,2-dioxane

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H-1 proton NMR spectroscopy - spectra index

Students and teachers please note my explanation of the proton NMR spectrum of 1,2-dioxane is designed for advanced, but pre-university, chemistry courses.

The chemical shift δ splitting pattern effects for 1,2-dioxane 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 1,2-dioxane 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 1,2-dioxane molecule.

The most common solvent used for investigating the 1H NMR spectrum of compounds like 1,2-dioxane, 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 - 1,2-dioxane here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of 1,2-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 1,2-dioxane molecule.

Interpreting the H-1 NMR spectrum of 1,2-dioxane

In terms of spin-spin coupling from the possible proton magnetic orientations, for 1,2-dioxane I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. R-CH2-CH2-X, protons.

For relatively simple molecules, the low resolution H-1 NMR spectrum of 1,2-dioxane is a good starting point (low resolution diagram above).

The hydrogen atoms (protons) of 1,2-dioxane occupy 2 different chemical environments so that the low resolution NMR spectra should show 2 principal 1H peaks of different H-1 NMR chemical shifts in the proton ratio of 4:4 observed as a integrated proton ratio of 1:1 (diagram above for 1,2-dioxane).

Chemical shifts (a) to (b) on the H-1 NMR spectrum diagram for 1,2-dioxane.

Although there are 8 hydrogen atoms in the molecule, there are only 2 possible different chemical environments for the hydrogen atoms in 1,2-dioxane molecule.

The integrated signal proton ratio 1:1 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 1,2-dioxane.

The high resolution 1H NMR spectrum of 1,2-dioxane

The high resolution spectra of 1,2-dioxane shows ? groups of proton resonances and in the ? ratio expected from the structural formula of 1,2-dioxane.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 1,2-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 1,2-dioxane below.

So, using the chemical shifts and applying the n+1 rule to 1,2-dioxane and make some predictions using some colour coding! (In problem solving you work the other way round!)

(a) 1H Chemical shift 3.55 ppm CH2 protons nearest the oxygen atoms

These CH2 protons are equivalent to each other but the a CH2 protons are split by the other b CH2 protons into a 1:2:1 triplet (n+1 = 3).

Because of the O-O peroxide linkage, the other CH2 protons are the only adjacent protons to cause spin-spin coupling and resonance line splitting.

Evidence for the presence of a CH2 group in the molecule of 1,2-dioxane

(b) 1H Chemical shift 1.45 ppm CH2 protons furthest the oxygen atoms

The b CH2 protons are split by the other a CH2 protons into a 1:2:1 triplet (n+1 = 3).

Evidence for the presence of a 2nd CH2 group in the molecule of 1,2-dioxane.

Take care in this interpretation

Due to the symmetry of the 1,2-dioxane, the b CH2 protons are both adjacent and equivalent and so do NOT cause splitting of each other's 1H NMR resonance. So, you observe a triplet not a 1:4:6:4:1 quintet of peaks.

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 1,2-dioxane.

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Links associated with 1,2-dioxane

The infrared spectrum of 1,2-dioxane (a cyclic peroxide), not available?

The infrared spectrum of 1,3-dioxane (a cyclic ether)

The infrared spectrum of 1,4-dioxane (a cyclic ether)

The mass spectrum of 1,2-dioxane (a cyclic peroxide), not available?

The mass spectrum of 1,3-dioxane (a cyclic ether)

The mass spectrum of 1,4-dioxane (a cyclic ether)

The H-1 spectrum of 1,2-dioxane (a cyclic peroxide)

The H-1 spectrum of 1,3-dioxane (a cyclic ether)

The H-1 spectrum of 1,4-dioxane (a cyclic ether)

The C-13 spectrum of 1,2-dioxane (a cyclic peroxide)

The C-13 spectrum of 1,3-dioxane (a cyclic ether)

The C-13 spectrum of 1,4-dioxane (a cyclic ether)

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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