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-2-ol here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of propan-2-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-2-ol molecule.

Interpreting the H-1 NMR spectrum of propan-2-ol  (2-propanol, isopropyl alcohol)

For relatively simple molecules, the low resolution H-1 NMR spectrum of propan-2-ol is a good starting point.

The hydrogen atoms (protons) of propan-2-ol occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 peaks of different H-1 NMR chemical shifts (diagram above for propan-2-ol).

(CH₃)₂CHOH  or  CH₃CH(OH)CH₃

Note the integrated proton ratio of 6:1:1 of the 3 colours of the protons in the 3 chemically different environments in the propan-2-ol molecule.

Although there are 8 hydrogen atoms in the molecule, there only 3 possible chemical environments for the hydrogen atoms in propan-2-ol molecule.

The proton ratio of 6:1:1 observed in the 1H NMR spectrum, corresponds with the structural formula of propan-2-ol.

The high resolution spectrum of propan-2-ol

All low and high resolution spectra of propan-2-ol show 3 groups of protons and in the ratio expected from the formula of propan-2-ol.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of propan-2-ol - 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 propan-2-ol below.

So, using the chemical shifts and applying the n+1 rule to propan-2-ol

(a) Chemical shift 1.20 ppm the two CH₃ groups of protons (6 protons)

The single CH proton splits the CH₃ resonance into a 1:1 doublet (n+1 = 2).

Evidence for the presence of a CH group in the molecule of propan-2-ol

(b) Chemical shift 4.01 ppm the lone CH proton (1 proton)

The single CH proton is split by the 6 methyl protons into a 1:6:15:20:15:6:1 septet (n+1 = 7), in terms of the relative intensities of the H-1 NMR resonance lines.

Evidence for the presence a CH₃-CH_x-CH₃ grouping in the molecule of propan-2-ol (x = 2 or 1 as in the case of propan-2-ol).

(c) Chemical shift 2.16 ppm the lone OH proton (1 proton)

Generally speaking, unless ultra dry and very high resolution, the hydroxyl proton resonance is not split and neither does it cause a splitting effect itself (see note at end).

Therefore you see a singlet resonance.

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-2-ol, all you usually see in the H-1 NMR spectrum is the mutual splitting of the CH 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.
	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.
	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.

The chemistry of ALCOHOLS revision notes INDEX

The infrared spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

The mass spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

The C-13 NMR spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

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

ALL SPECTROSCOPY INDEXES

All Advanced Organic Chemistry Notes

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