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Advanced Organic Chemistry: H-1 NMR spectrum of propan-1-ol

The H-1 hydrogen-1 (proton) NMR spectrum of propan-1-ol (1-propanol)

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 propan-1-ol

See also comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 isomers of C3H8O

low and high resolution H-1 proton nmr spectrum of propan-1-ol analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 1-H nmr for 1-propanol 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 - propan-1-ol here.

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

Propan-1-ol C3H8O, alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b

Interpreting the H-1 NMR spectrum of propan-1-ol

For relatively simple molecules, the low resolution H-1 NMR spectrum of propan-1-ol is a good starting point.

The hydrogen atoms (protons) of propan-1-ol occupy 4 different chemical environments so that the low resolution NMR spectra should show 4 peaks of different H-1 NMR chemical shifts (diagram above for propan-1-ol).

CH3CH2CH2OH 

Note the ratio 3:2:2:1 of the four colours of the protons in the four chemically different environments

Although there are 8 hydrogen atoms in the molecule, there only 4 possible chemical environments for the hydrogen atoms in propan-1-ol molecule.

The integrated proton ratio of 3:2:2:1 observed, corresponds with the structural formula of propan-1-ol.

The high resolution spectrum of propan-1-ol

All low and high resolution spectra of propan-1-ol show four groups of protons and in the ratio expected from the formula of propan-1-ol.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of propan-1-ol - since the peak' is at the apex of a band of H-1 NMR resonances due to spin - spin filed splitting effects - see high resolution notes on propan-1-ol below.

So, using the chemical shifts and applying the n+1 rule to propan-1-ol

(a) Chemical shift 0.94 ppm alkyl CH3 protons (blue)   CH3CH2CH2OH

The CH3 proton resonance line is split in to a 1:2:1 triplet by the adjacent CH2 protons (2 protons, n+1 = 3 = triplet)

Evidence for the presence of a CH2 group in the molecule of propan-1-ol

(b) Chemical shift 1.57 ppm alkyl CH2 protons (purple)   CH3CH2CH2OH

The left CH2 proton resonance line is split in to a 1:6:15:20:15:6:1 sextet by the adjacent CH3 and CH2 protons (5 protons, n+1 = 6 = sextet)

Evidence for the presence of a propyl group in the molecule of propan-1-ol

(c) Chemical shift 3.58 alkyl CH2 protons (green)   CH3CH2CH2OH

The 'right-hand' CH2 proton resonance line is split in to a 1:2:1 triplet by the 'left-hand' adjacent CH2 protons (2 protons, n+1 = 3 = triplet)

Evidence for the presence of a 2nd CH2 group in the molecule of propan-1-ol

(d) Chemical shift 2.26 OH hydroxyl proton (brown)   CH3CH2CH2OH

The hydroxyl proton is not split by the adjacent CH2 protons AND neither does it split the CH2 proton resonances.

So all you see is a singlet peak.

Note on the OH proton resonance

If the alcohol is impure, containing water or any source of labile protons, because water and the alcohol exchange protons e.g.

R-O-H  +  H-O-H    R-O-H  +  H-O-H

This means the CH2 protons no longer experience a 'simple' local field from one singlet proton from two possible orientations, but, over a finite period, experience the averaging effect of exchanging protons.

This removes the spin - spin coupling effect and the OH proton resonance just shows up as a singlet if the butan-1-ol contains even a trace of water (or acid).

This sort of exchange cannot happen with the alkyl protons, but is common with molecules containing a hydroxylic (OH) hydrogen atom like alcohols and carboxylic acids.

Not only that, you also get proton transfer between the alcohol molecules i.e.

R-O-H  +  H-O-R    R-O-H  +  H-O-R

which gives the same effect as traces of water of acid.

So, in propan-1-ol, all you usually see in the H-1 NMR spectrum is the mutual splitting of the CH2 and CH3 proton resonances plus a singlet line for the OH proton resonance.

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 isomers of C3H8O

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 propan-1-ol, propan-2-ol and methoxyethane image sizes.

infrared spectrum of ethoxyethane wavenumbers cm-1 functional group detection fingerprint pattern identification of  diethyl ether doc brown's advanced organic chemistry revision notes I wasn't able to obtain an infrared spectrum for methoxyethane, so I've added the infrared spectrum of ethoxyethane to enable a few comparisons with two aliphatic alcohols

Comparing the infrared spectra of propan-1-ol, propan-2-ol and methoxyethane

Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C3H8O

Propan-1-ol, propan-2-ol and methoxyethane exemplify infrared spectra of the lower members of the homologous series of aliphatic alcohols and ethers

INFRARED SPECTRA (above): There are, as expected, differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, but most absorptions for all three molecules are the various C-O and the many C-H vibrational modes. However, there is one characteristic distinguishing absorption only present in the infrared spectra of alcohols, but not in ethers, that is the broad O-H stretching vibration peaking at ~3350 cm-1. There is also another broad absorption band (origin?) peaking at ~650 cm-1 in the alcohol spectra, but not in the ether spectra.

Comparing the mass spectra of propan-1-ol, propan-2-ol and methoxyethane

Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C3H8O

Propan-1-ol, propan-2-ol and methoxyethane exemplify the mass spectra of the lower members of the homologous series of aliphatic alcohols and ethers

MASS SPECTRA (above): The base ion peaks are m/z 45 for propan-2-ol and methoxyethane, but that of propan-1-ol is m/z 31. Many of the fragmentation ions are common to all three spectra. The m/z 45 ion is peak is much smaller in the propan-1-ol spectrum compared to the other two.

Comparing the 1H proton NMR spectra of propan-1-ol, propan-2-ol and methoxyethane

Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C3H8O

Propan-1-ol, propan-2-ol and methoxyethane exemplify the 1H proton NMR spectra of the lower members of the homologous series of aliphatic alcohols and ethers

1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different integrated proton ratios for the different 1H chemical environments i.e. the proton ratios are as follows: propan-1-ol 3:2:2:1; propan-2-ol 6:1:1 and methoxyethane 3:2:3. Therefore, all three can be distinguished by their 1H NMR spectra. The sextet in the 1H NMR spectrum of propan-1-ol is characteristic of a propyl group, absent in the other two NMR spectra.

Comparing the carbon-13 NMR spectra of propan-1-ol, propan-2-ol and methoxyethane

Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C3H8O

Propan-1-ol, propan-2-ol and methoxyethane exemplify the carbon-13 NMR spectra of members of  the lower members of the homologous series of aliphatic alcohols and ethers

13C NMR SPECTRA (above): The 13C NMR spectra of propan-1-ol and methoxyethane show three different 13C NMR chemical shifts, but propan-2-ol can be distinguished from the other two by exhibiting only two chemical shift lines. You would need other spectral data to distinguish propan-1-ol and methoxyethane.

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

Key words & phrases: 1-propanol n-propyl alcohol Interpreting the proton H-1 NMR spectra of propan-1-ol, low resolution & high resolution proton nmr spectra of propan-1-ol, H-1 nmr spectrum of propan-1-ol, understanding the hydrogen-1 nmr spectrum of propan-1-ol, explaining the line splitting patterns in the high resolution H-1 nmr spectra of propan-1-ol, revising the H-1 nmr spectrum of propan-1-ol, proton nmr of propan-1-ol, ppm chemical shifts of the H-1 nmr spectrum of propan-1-ol, 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 propan-1-ol, how to work out the number of chemically different protons in the structure of the propan-1-ol organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of propan-1-ol using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of propan-1-ol deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of propan-1-ol examining the 1H nmr spectrum of  propan-1-ol analysing the 1-H nmr spectrum of propan-1-ol how do you sketch and interpret the H-1 NMR spectrum of propan-1-ol 1-propanol n-propyl alcohol

isomer of molecular formula C3H8O Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of propan-1-ol 1-propanol. The proton ratio in the 1H NMR spectrum of propan-1-ol 1-propanol. Deducing the number of different chemical environments of the protons in the propan-1-ol 1-propanol molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of propan-1-ol 1-propanol. Analysing the high resolution 1H NMR spectrum of propan-1-ol 1-propanol. Analysing the low resolution 1H NMR spectrum of propan-1-ol 1-propanol. You may need to know the relative molecular mass of propan-1-ol 1-propanol to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of propan-1-ol 1-propanol. Revision notes on the proton NMR spectrum of propan-1-ol 1-propanol. Matching and deducing the structure of the propan-1-ol 1-propanol molecule from its hydrogen-1 NMR spectrum. Proton NMR spectroscopy of aliphatic alcohols, 1H NMR spectra of propan-1-ol 1-propanol, an isomer of molecular formula C3H8O


Links associated with propan-1-ol (1-propanol)

The chemistry of ALCOHOLS revision notes INDEX

The infrared spectrum of Propan-1-ol (1-propanol, n-propyl alcohol)

The mass spectrum of Propan-1-ol (1-propanol, n-propyl alcohol)

The C-13 NMR spectrum of Propan-1-ol (1-propanol, n-propyl alcohol)

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

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