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Advanced Organic Chemistry: H-1 NMR spectrum of propane

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

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 propane

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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

low and high resolution H-1 proton nmr spectrum of propane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 1-H nmr for propane 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 shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the hydrogen atoms in an organic molecule - propane here.

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

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

Propane C3H8, alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b

Interpreting the H-1 NMR spectrum of propane (dissolved in CDCl3)

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

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

CH3CH2CH3 

Note the ratio 6:2 = 3:1 of the two colours of the protons in the two chemically different environments

Although there are 8 hydrogen atoms in the molecule, there only 2 possible chemical environments for the hydrogen atoms in propane molecule.

The overall proton ratio 3:1 observed, corresponds with the structural formula of propane.

The high resolution H-1 NMR spectrum of propane

All low and high resolution spectra of propane show two groups of protons and in the ratio 3:1 expected from the formula of propane.

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

So, using the chemical shifts and applying the n+1 rule to propane

Chemical shift (a) 0.90 ppm, the two groups of CH3 protons: CH3CH2CH3

This proton resonance 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 propane

Chemical shift (b) 1.34 ppm, the one group of CH2 protons:  CH3CH2CH3

The central CH2 group protons are split on either side by a group of CH3 protons (6 protons in total) into a 1:6:15:20:15:6:1 septet (n+1 = 7)

Evidence for the presence of a two CH3 groups separated by a carbon atom with at least one proton on it in the molecule of propane i.e. CH3-CHx-CH3 grouping.


Number of protons 1H causing splitting Splitting pattern produced from the n+1 rule 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: Interpreting the proton H-1 NMR spectra of propane C3H8 CH3CH2CH3, low resolution & high resolution proton nmr spectra of propane, H-1 nmr spectrum of propane, understanding the hydrogen-1 nmr spectrum of propane, explaining the line splitting patterns in the high resolution H-1 nmr spectra of propane, revising the H-1 nmr spectrum of propane, proton nmr of propane, ppm chemical shifts of the H-1 nmr spectrum of propane, 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 propane, how to work out the number of chemically different protons in the structure of the propane organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of propane using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of propane deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of propane examining the 1H nmr spectrum of  propane analysing the 1-H nmr spectrum of propane how do you sketch and interpret the H-1 NMR spectrum of propane Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of propane. The proton ratio in the 1H NMR spectrum of propane. Deducing the number of different chemical environments of the protons in the propane molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of propane. Analysing the high resolution 1H NMR spectrum of propane. Analysing the low resolution 1H NMR spectrum of propane. You may need to know the relative molecular mass of propane to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of propane. Revision notes on the proton NMR spectrum of propane. Matching and deducing the structure of the propane molecule from its hydrogen-1 NMR spectrum.


Links associated with propane

The chemistry of ALKANES revision notes INDEX

The infrared spectrum of propane  (Please read 8 points at the top of the 1H NMR index page)

The mass spectrum of propane

The C-13 NMR spectrum of propane

H-1 proton NMR spectroscopy index

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