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Advanced Organic Chemistry: 1H NMR spectrum of propene ('propylene')

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Interpreting the H-1 hydrogen-1 (proton) NMR spectrum of propene

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 propene

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H-1 proton NMR spectroscopy - spectra index

See also comparing the infrared, mass, 1H NMR and 13C NMR spectra of propane, cyclopropane and propene

1H proton nmr spectrum of propene low/high resolution diagrams C3H6 CH3CH=CH2 analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for propene 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 - propene here.

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

Propene, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b, alkenes structure and naming (c) doc b

Interpreting the H-1 NMR spectrum of propene

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

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

The 6 hydrogen atoms (protons) of propene appear to occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 principal peaks of different H-1 NMR chemical shifts (diagram above for propene).

CH2=CH-CH3

Note the proton ratio of 2:1:3 of the 3 colours of the 6 protons of propene in the 3 chemically different proton environments

Chemical shifts (a)/(b) : (c) : (d) on the H-1 NMR spectrum diagram for propene.

The high resolution 1H NMR spectrum of propene

However, the high resolution spectra of propene shows 4 groups of proton resonances and in the 1:1:1:3 ratio expected from the structural formula of propene.

alkenes structure and naming (c) doc bThe two resonances for the protons of the end =CH2 group are very slightly different due to these two protons experiencing slightly different shielding field effects due to the asymmetric grouping at the other end of the C=C bond. (It doesn't matter which way round you draw the structure of propene!)

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

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

For propene this is actually quite tricky and NOT what you might expect because of the slightly different chemical shifts of the H2C= end protons in propene, meaning they are NOT equivalent.

Resonance (a) and (b) 1H Chemical shift: CH2=CH-CH3

1H NMR chemical shifts of 5.00 and 4.93 ppm.

You might think that the resonance for the CH2 protons would be split into a doublet by the lone CH proton (n+1 = 2), but you can see from the higher resolution spectrum, there are quite a few lines!

What us happening is that each CH2 proton is split by the other proton and by the lone CH proton.

You therefore have two triplets overlapping each other (two n+1 = 3).

Resonance (c) 1H Chemical shift: CH2=CH-CH3

1H NMR chemical shift of 5.84 ppm.

Again, we have problems with interpretation and you might expect the CH resonance to be split into a sextet by the adjacent CH2 and CH3 protons on either side (n+1 = 6).

BUT not so, the CH proton resonance is split by the CH3 proton field but also separately by the individual CH2 protons, to give two overlapping quintets (two n+1 = 5).

Resonance (d) 1H Chemical shift: CH2=CH-CH3

1H NMR chemical shift of 1.65 ppm.

This is split into a doublet by the adjacent CH group proton (n+1 = 2), with no complications!

Evidence of a -CH- grouping in the molecule.


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
Comparing the infrared, mass, 1H NMR and 13C NMR spectra of propane, cyclopropane and propene

NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original ethane and ethene image sizes.

Comparing the infrared spectra of propane, propene and cyclopropane.

Cyclopropane and propene are structural isomers of molecular formula C3H6.

Propane and propene exemplify the infrared spectra of lower members of  the alkane and alkene homologous series of CnH2n+2 and CnH2n hydrocarbon molecules where n = 3.

INFRARED SPECTRA (above): Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, the most striking differences are: (i) propene shows the characteristic absorption at ~1700 cm-1 for the C=C stretching vibrations, absent in the other two spectra, (ii) cyclopropane shows an absorption band at 2200 cm-1, absent in the other two spectra, (iii) propane has an absorption band at ~750 cm-1, absent in the other two spectra.

Comparing the mass spectra of propane, propene and cyclopropane.

Cyclopropane and propene are structural isomers of molecular formula C3H6.

Propane and propene exemplify the mass spectra of lower members of  the alkane and alkene homologous series of CnH2n+2 and CnH2n hydrocarbon molecules where n = 3.

MASS SPECTRA (above): All three hydrocarbons show some similarities in their mass spectra e.g. m/z ions 26 to 28 for [C2Hx]+ (x = 2 to 4) and m/z 14 and 15 ions - but these are found in most aliphatic hydrocarbon spectra. The molecular ion peaks will be the same for the isomeric propene and cyclopropane (m/z 42) but that of propane will be 2 mass units higher at m/z 44. The base ion peak m/z values are all different, propane 29, propene 41 and cyclopropane 42.

Comparing the 1H proton NMR spectra of propane, propene and cyclopropane.

Cyclopropane and propene are structural isomers of molecular formula C3H6.

Propane and propene exemplify the 1H proton NMR spectra of lower members of  the alkane and alkene homologous series of CnH2n+2 and CnH2n hydrocarbon molecules where n = 3.

1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios i.e. propane 3:1 (actually 6:2 in the molecule), propene 2:1:3 (spectrum and molecule) and cyclopropane just a singlet for the six protons, so all three can be distinguished from each other by their 1H NMR spectra..

Comparing the carbon-13 NMR spectra of propane, propene and cyclopropane.

Cyclopropane and propene are structural isomers of molecular formula C3H6.

Propane and propene exemplify the carbon-13 NMR spectra of lower members of  the alkane and alkene homologous series of CnH2n+2 and CnH2n hydrocarbon molecules where n = 3.

13C NMR SPECTRA (above): The 13C NMR spectra of the three molecules show different numbers of carbon-13 chemical environments i.e propane 2, propene 3 and cyclopropane only 1, so all three could be distinguished from each other.

Key words & phrases: C3H6 H2C=CHCH3 CH3CH=CH2 CH2=CHCH3 Interpreting the proton H-1 NMR spectra of propene, low resolution & high resolution proton nmr spectra of propene, H-1 nmr spectrum of propene, understanding the hydrogen-1 nmr spectrum of propene, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of propene, revising the H-1 nmr spectrum of propene, proton nmr of propene, ppm chemical shifts of the H-1 nmr spectrum of propene, 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 propene, how to work out the number of chemically different protons in the structure of the propene organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of propene using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of propene deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of propene examining the 1H nmr spectrum of  propene analysing the 1-H nmr spectrum of propene how do you sketch and interpret the H-1 NMR spectrum of propene interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of propene  assignment of chemical shifts in the proton 1H NMR spectrum of propene formula explaining spin-spin coupling for line splitting for propene alkene functional group propylene Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of propene. The proton ratio in the 1H NMR spectrum of propene. Deducing the number of different chemical environments of the protons in the propene molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of propene. Analysing the high resolution 1H NMR spectrum of propene. Analysing the low resolution 1H NMR spectrum of propene. You may need to know the relative molecular mass of propene to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of propene. Revision notes on the proton NMR spectrum of propene. Matching and deducing the structure of the propene molecule from its hydrogen-1 NMR spectrum.


Links associated with propene

The chemistry of ALKENES revision notes INDEX

The infrared spectrum of propene ('propylene')

The mass spectrum of propene ('propylene')

The C-13 NMR spectrum of propene ('propylene')

H-1 proton NMR spectroscopy index  (Please read 8 points at the top of the 1H NMR index page)

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