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Advanced Organic Chemistry: 1H NMR spectrum of phenol

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

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 phenol

1H proton nmr spectrum of phenol low/high resolution diagrams C6H6O C6H5OH analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for phenol 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 - phenol here.

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

PhenolC6H6OC6H5OH, (c) doc b(c) doc b

Interpreting the H-1 NMR spectrum of phenol

In terms of spin-spin coupling from the possible proton magnetic orientations, for phenol I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH protons etc. but no splitting of or by the hydroxyl OH proton.

You need high resolution H-1 NMR spectrum of phenol to detect the different proton environments.

The 6 hydrogen atoms (protons) of phenol occupy 4 different chemical environments so that the high resolution NMR spectra should show 4 principal peaks of different H-1 NMR chemical shifts (diagram above for phenol).

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

Although there are 6 hydrogen atoms in the molecule, there are only 4 possible different chemical environments for the hydrogen atoms in phenol molecule.

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

The high resolution 1H NMR spectrum of phenol

The high resolution spectra of phenol shows 4 groups of proton resonances and in the 2:2:1:1 ratio expected from the structural formula of phenol.

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

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

Resonance (a) 1H Chemical shift for OH proton, 5.35 ppm.

This is observed as a singlet, there are no adjacent protons on the C1 carbon atom of the benzene.

aromatic benzene ring carbon atom positions in phenol 1H proton NMR spectroscopy Ring positions in monosubstituted benzene compounds.

One of the problems in interpreting NMR spectra is that the benzene ring CH proton 1H resonances (converted to chemical shifts) are often quite close together e.g. as in the 1H NMR spectrum of phenol.

Resonance (b) 1H Chemical shift for a CH protons on C2/C6, 6.84 ppm.

This 1H NMR resonance applies to the protons on the equivalent carbon atoms C2 and C6.

This resonance is split into a 1:1 doublet by the adjacent C3 or C5 CH proton (n+1 = 2).

Note there is no proton on carbon atom C1 that might increase the splitting effect.

Evidence for the presence of a CH group in the molecule of phenol

Resonance (c) 1H Chemical shift for a CH protons on C3/C5, 7.24 ppm.

This 1H NMR resonance applies to the protons on the equivalent carbon atoms C3 and C5.

This resonance is split into a 1:2:1 triplet by the adjacent CH protons on C4 and C6 on either side (n+2 = 3).

Resonance (d) 1H Chemical shift for a CH proton on C4, 6.93 ppm.

This 1H NMR resonance applies to the proton on carbon atom C4.

This resonance is split into a 1:2:1 triplet by the adjacent CH protons on C3 and C5 on either side (n+2 = 3).


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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