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-iodobutane here.

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

Interpreting the H-1 NMR spectrum of 1-iodobutane

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

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

The 9 hydrogen atoms (protons) of 1-iodobutane occupy 4 different chemical environments so that the low resolution NMR spectra should show 4 principal resonance peaks of different H-1 NMR chemical shifts (diagram above for 1-iodobutane).

CH₃CH₂CH₂CH₂I

Note the proton ratio 3:2:2:2 of the 4 colours of the 9 protons of 1-iodobutane in the 4 chemically different proton environments

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

Although there are 9 hydrogen atoms in the molecule, the proton NMR spectrum shows there are only 4 possible different chemical environments for the hydrogen atoms in 1-iodobutane molecule.

The integrated proton signal ratio 3:2:2:2 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 1-iodobutane.

The high resolution 1H NMR spectrum of 1-iodobutane

The high resolution spectra of 1-iodobutane shows 4 groups of proton resonances and in the 3:2:2:2  ratio expected from the structural formula of 1-iodobutane, but we can now consider the splitting of resonance lines from the spin-spin coupling in the molecule of 1-iodobutane.

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

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

¹H NMR resonance (a) ¹H Chemical shift 0.93 ppm: CH₃CH₂CH₂CH₂I

This resonance is split into a 1:2:1 triplet by the adjacent CH₂ protons (n+1 = 3).

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

¹H NMR resonance (b) ¹H Chemical shift 1.42 ppm: CH₃CH₂CH₂CH₂I

This resonance is split into a 1:5:10:10:5:1 sextet by the adjacent CH3 and CH2 protons (on either side, so n=1 = 6).

Evidence for the presence of a ? group in the molecule of 1-iodobutane

¹H NMR resonance (c) ¹H Chemical shift 1.80 ppm: CH₃CH₂CH₂CH₂I

This resonance is split into a 1:4:6:4:1 quintet by the adjacent CH₂ protons on either side, so n=1 = 5.

Evidence for the presence of a CH₂-CH_x-CH₂ grouping in the molecule of 1-iodobutane (x = 1, or 2, as in this case).

¹H NMR resonance (d) ¹H Chemical shift 3.20 ppm: CH₃CH₂CH₂CH₂I

This resonance is split into a 1:2:1 triplet by the adjacent CH₂ protons (n+1 = 3).

Evidence for the presence of a at least one other CH₂ group in the molecule of 1-iodobutane (see resonance (a) above).

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

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.