Advanced Organic Chemistry: 1H NMR spectrum of iodoethane

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Interpreting the H-1 (proton) NMR spectrum of iodoethane (ethyl iodide)

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 iodoethane

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H-1 proton NMR spectroscopy - spectra index

1H proton nmr spectrum of iodoethane low/high resolution diagrams C2H5I CH3CH2I analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for ethyl iodide explaining spin-spin coupling for line splitting doc brown's advanced organic chemistry revision notes

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 - iodoethane here.

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

iodoethane, C2H5I, CH3CH2I, CH3-CH2-I

Interpreting the H-1 NMR spectrum of iodoethane

In terms of spin-spin coupling from the possible proton magnetic orientations, for iodoethane I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH2-CH3, protons etc.

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

The 5 hydrogen atoms (protons) of iodoethane occupy 2 different chemical environments so that the low resolution NMR spectra should show 2 principal peaks of different H-1 NMR chemical shifts (diagram above for iodoethane).

CH3-CH2-I

Note the integrated proton ratio of 3:2 of the 2 colours of the 2 protons of iodoethane in the 2 chemically different proton environments

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

Although there are 5 hydrogen atoms in the molecule, the proton NMR spectrum shows there are only 2 possible different chemical environments for the hydrogen atoms in iodoethane molecule.

The integrated signal proton ratio 3:2 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of iodoethane.

The high resolution 1H NMR spectrum of iodoethane

The high resolution spectra of iodoethane still shows 2 groups of proton resonances and in the 3:2 ratio expected from the structural formula of iodoethane, but we can now consider the splitting of resonance lines from the spin-spin coupling in the molecule of iodoethane.

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

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

Resonance (a) 1H Chemical shift 1.85 ppm: CH3CH2I

The methyl group proton resonance is split by the CH2 group protons into a 1:2:1 triplet (n+1 = 3).

Evidence for the presence of a CH2 group in the molecule of iodoethane

Resonance (b) 1H Chemical shift 3.19 ppm: CH3CH2I

The CH2 group proton resonance is split by the methyl group protons into a 1:3:3:1 quartet (n+1 = 4).

Evidence for the presence of a CH3 group in the molecule of iodoethane

Note the decreasing effect on the 1H chemical shift as the proton is further from the more electronegative oxygen and nitrogen bromine chlorine atoms iodoethane.

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

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Links associated with iodoethane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The infrared spectrum of iodoethane (ethyl iodide)

The mass spectrum of iodoethane (ethyl iodide)

The C-13 NMR spectrum of iodoethane (ethyl iodide)

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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