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 - 1-iodo-2-methylpropane here.

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

Interpreting the H-1 NMR spectrum of 1-iodo-2-methylpropane

In terms of spin-spin coupling from the possible proton magnetic orientations, for 1-iodo-2-methylpropane I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH₃, -CH-CH₂- protons etc.

For relatively simple molecules, the low resolution H-1 NMR spectrum of 1-iodo-2-methylpropane is a good starting point (low resolution diagram above).

The 9 hydrogen atoms (protons) of 1-iodo-2-methylpropane occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 principal resonance peaks of different H-1 NMR chemical shifts (diagram above for 1-iodo-2-methylpropane).

(CH₃)₂CHCH₂I

Note the proton ratio 6:2:1 of the 3 colours of the 9 protons of 1-iodo-2-methylpropane in the 3 chemically different 1H proton environments

Chemical shifts δ (a) to (c) on the H-1 NMR spectrum diagram for 1-iodo-2-methylpropane.

Although there are 9 hydrogen atoms in the molecule, the proton NMR spectrum shows there are only 3 possible different chemical environments for the hydrogen atoms in 1-iodo-2-methylpropane molecule.

The integrated proton signal ratio of 6:2:1 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 1-iodo-2-methylpropane.

The high resolution 1H NMR spectrum of 1-iodo-2-methylpropane

The high resolution spectra of 1-iodo-2-methylpropane shows 3 groups of proton resonances and in the 6:2:1 ratio expected from the structural formula of 1-iodo-2-methylpropane, but we can now consider the splitting of resonance lines from the spin-spin coupling in the molecule of 1-iodo-2-methylpropane.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 1-iodo-2-methylpropane - 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 1-iodo-2-methylpropane below.

So, using the chemical shifts and applying the n+1 rule to 1-iodo-2-methylpropane and make some predictions using some colour coding! (In problem solving you work the other way round!)

¹H NMR resonance (a) ¹H Chemical shift δ 1.02 ppm: (CH₃)₂CHCH₂I

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

The six methyl protons are all equivalent due to the symmetry of the 1-iodo-2-methylpropane molecule.

Evidence for the presence of a CH group in the molecule of 1-iodo-2-methylpropane

¹H NMR resonance (b) ¹H Chemical shift δ 1.74 ppm: (CH₃)₂CHCH₂I

This resonance is split into a nonet (9) of resonance lines by protons of the two adjacent methyl groups AND the CH₂ group (n+1 = 9).

Evidence for the presence of a (CH₃)₂CHCH₂ grouping in the molecule of 1-iodo-2-methylpropane

¹H NMR resonance (c) ¹H Chemical shift δ 3.14 ppm: (CH₃)₂CHCH₂I

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

Evidence for the presence of a CH group in the molecule of 1-iodo-2-methylpropane

Note the decreasing effect on the ¹H chemical shift as the proton is further from the more electronegative iodine atom in 1-iodo-2-methylpropane.

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 4 halogenoalkane isomers of C4H9I 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 1-iodobutane, 2-iodobutane, 1-iodo-2-methylpropane and 2-iodo-2-methylpropane image sizes.  These four molecules are structural isomers of molecular formula C4H9I and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower aliphatic halogenoalkanes (haloalkanes, alkyl halides, iodoalkanes, alkyl iodides).
INFRARED SPECTRA (above): Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, there are no other great striking differences, but each could be identified from its infrared spectrum.
MASS SPECTRA (above): All four give the parent molecular ion of m/z 184, but it is only a relatively tiny peak for 2-iodo-2-methylpropane. All four give the base ion peak of m/z 57. All four give prominent peaks for m/z ions 29 and 41 and all give a tiny peak from an ionised iodine atom at m/z 127. They look quite similar to me and lack a clear fingerprint fragmentation pattern.
1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios i.e.1-iodobutane four peaks 3:2:2:2, 2-iodobutane four peaks 3:3:2:1, 1-iodo-2-methylpropane three peaks 6:2:1 and 2-iodo-2-methylpropane one peak '1' (effectively no ratio involved), so all four molecular structures can be distinguished from each other by their 1H NMR spectra proton ratios, numbers of peaks and (n+1) rule splitting patterns.
13C NMR SPECTRA (above): The 13C NMR spectra of the four molecules show various numbers of carbon-13 chemical environments i.e 1-iodobutane and 2-iodobutane show four 13C NMR resonances, 1-iodo-2-methylpropane three 13C NMR resonances and 2-iodo-2-methylpropane only two 13C resonances. Therefore 1-iodo-2-methylpropane and 2-iodo-2-methylpropane can be distinguished from the other three by their number of resonances in their 13C NMR spectra, but 1-iodobutane and 2-iodobutane cannot be distinguished from each other from their number of 13C NMR resonance lines - other data would be required.