Advanced Organic Chemistry: 1H NMR spectrum of propan-2-amine

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Interpreting the H-1 hydrogen-1 (proton) NMR spectrum of propan-2-amine (2-aminopropane, 2-propanamine, 2-propylamine, isopropylamine)

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-2-amine (2-aminopropane)

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H-1 proton NMR spectroscopy - spectra index

1H proton nmr spectrum of propan-2-amine (2-aminopropane) low/high resolution diagrams C3H9N (CH3)2CHNH2 analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for isopropylamine 2-propylamine 2-propanamine 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 - propan-2-amine (2-aminopropane) here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of propan-2-amine (2-aminopropane) 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-amine (2-aminopropane) molecule.

propan-2-amine, 2-aminopropane, 2-propylamine, 2-propanamine, isopropylamine, (c) doc b, (c) doc b

Interpreting the H-1 NMR spectrum of propan-2-amine (2-aminopropane)

In terms of spin-spin coupling from the possible proton magnetic orientations, for propan-2-amine (2-aminopropane) I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH3 protons (but see note on problems with N-H proton resonance).

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

The hydrogen atoms (protons) of propan-2-amine (2-aminopropane) occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 principal peaks of different H-1 NMR chemical shifts (diagram above for propan-2-amine (2-aminopropane) in the ratio 6:1:2

(CH3)2CHNH2

Note the proton ratio 6:1:2 of the 3 colours of the 9 protons of propan-2-amine (2-aminopropane) in the 3 chemically different proton environments

Chemical shifts (a) to (c) on the H-1 NMR spectrum diagram for propan-2-amine (2-aminopropane).

Although there are 9 hydrogen atoms in the molecule, there are only 3 possible different chemical environments for the hydrogen atoms in propan-2-amine (2-aminopropane) molecule.

The integrated signal proton ratio 6:1:2 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of propan-2-amine (2-aminopropane).

The high resolution 1H NMR spectrum of propan-2-amine (2-aminopropane)

The high resolution spectra of propan-2-amine (2-aminopropane) shows 3 groups of proton resonances and in the 6:1:2 ratio expected from the structural formula of propan-2-amine (2-aminopropane).

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

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

(a) 1H Chemical shift 1.07 ppm, methyl protons: (CH3)2CHNH2

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

All six protons are equivalent to each other.

Evidence for the presence of a CH group in the molecule of propan-2-amine (2-aminopropane)

(b) 1H Chemical shift 3.10 ppm, CH group proton: (CH3)2CHNH2

This resonance is split into a 1:6:15:20:15:6:1 septet by the methyl group protons (n+1 = 7), the amine group protons do not normally cause splitting.

Evidence for the presence of a CH3-CHx-CH3 grouping in the molecule of propan-2-amine (2-aminopropane)

(c) 1H Chemical shift 1.22 ppm, amine group protons: (CH3)2CHNH2

This resonance appears a singlet because amine proton resonances are not usually split by adjacent C-H protons.

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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Links associated with propan-2-amine (2-aminopropane)

The chemistry of ORGANIC NITROGEN COMPOUNDS revision notes INDEX

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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