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Advanced Organic Chemistry: 1H NMR spectrum of chloroethane

The H-1 hydrogen-1 (proton) NMR spectrum of chloroethane

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 chloroethane

C2H5Cl CH3CH2Cl low and high resolution 1H proton nmr spectrum of chloroethane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for ethyl chloride 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 - chloroethane here.

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

chloroethane   CH3CH2Cl   CH3-CH2-Cl

Interpreting the H-1 NMR spectrum of chloroethane

In terms of spin-spin coupling from the possible proton magnetic orientations, for chloroethane 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 chloroethane is a good starting point (low/high resolution diagrams above).

The hydrogen atoms (protons) of chloroethane 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 chloroethane).

CH3CH2Cl

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

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

Although there are 5 hydrogen atoms in the molecule, there are only 2 possible different chemical environments for the hydrogen atoms in chloroethane molecule.

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

The high resolution 1H NMR spectrum of chloroethane

All low and high resolution spectra of chloroethane show 2 groups of proton resonances and in the 3:2 ratio expected from the formula of chloroethane.

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

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

(a) 1H Chemical shift 1.49 ppm, CH3 protons: CH3CH2Cl

This 1H resonance is split by the CH2 protons into a 1:2:1 triplet (n+1 = 3)

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

(b) 1H Chemical shift 3.51 ppm, CH2 protons: CH3CH2Cl

This 1H resonance is split by the CH3 protons into a 1:3:3:1 quartet (n+1 = 4)

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

Note the increased effect on the 1H chemical shift of the protons on carbon atom nearest the most electronegative chlorine atom.


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 chloroethane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

H-1 proton NMR spectroscopy index

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