Advanced Organic Chemistry: H-1 NMR spectrum of propylamine

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H-1 hydrogen-1 (proton) NMR spectrum of propylamine (1-aminopropane)

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 propylamine

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H-1 proton NMR spectroscopy - spectra index

low and high resolution H-1 proton nmr spectrum of propylamine analysis interpretation of chemical shifts ppm spin spin line splitting diagram 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 shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the hydrogen atoms in an organic molecule - propylamine here.

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

propylamine, (1-aminopropane), C3H9N, (c) doc b , (c) doc b , (c) doc b

Interpreting the H-1 NMR spectrum of propylamine

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

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

CH3CH2CH2NH2

(Note the ratio 3:2:2:2 of the four colours of the protons in the four chemically different environments)

Although there are 9 hydrogen atoms in the molecule, there are only 4 possible chemical environment for the hydrogen atoms of propylamine.

The proton ratio 3:2:2:2 observed, corresponds with the structural formula of propylamine.

As you can see, the high resolution spectrum of propylamine is complex

So, using the chemical shifts and applying the n+1 rule to propylamine,

BUT the protons attached to the nitrogen atom do not usually cause a resonance splitting effect on protons on an adjacent carbon, and neither is their resonance split by adjacent carbon atom protons.

Chemical shift (a) methyl protons (blue)

At a chemical shift of 0.92 ppm the CH3 protons are split by the adjacent CH2 protons into a 1:2:1 triplet in terms of intensities (theoretically), n+2 = 3.

Evidence for the presence of a CH2 group in the molecule of propylamine

CH3CH2CH2NH2

Chemical shift (b) CH2 protons (purple)

The 1.45 ppm chemical shift:

From the n+1 rule, the 'left-hand' CH2 protons (H2) are split by CH3 protons (H3) and by the 'right-hand' CH2 protons (H2), (5 protons in total), into a 1:5:10:10:5:1 sextet of resonance lines (n+5 = 6).

This is pattern of resonances is a good indication of a propyl group (CH3CH2CH2).

CH3CH2CH2NH2

Chemical shift (c) CH2 protons (green)

The 2.65 ppm chemical shift:

The 'right-hand' CH2 protons (H2) resonances are split by the left CH2 protons (H2) into a 1:2:1 triplet of resonance lines (n+2 = 3). No splitting due to the NH2 protons.

CH3CH2CH2NH2

Chemical shift (d) NH2 protons (brown)

The 1.24 ppm chemical shift:

The amine group proton resonance is not split by the adjacent CH2 protons, so appears a singlet.

So what you observe is a singlet, which is actually two singlet resonances close together.

The lack of resonance splitting is due to exchange of protons between the amine group of the amine molecules which inhibits the coupling between amine group protons and any adjacent alky group protons - even a trace of water catalyses this effect.

Number of protons 1H causing splitting Splitting pattern produced from the n+1 rule 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

Key words & phrases: Interpreting the proton H-1 NMR spectra of propylamine, low resolution & high resolution proton nmr spectra of propylamine, H-1 nmr spectrum of propylamine, understanding the hydrogen-1 nmr spectrum of propylamine, explaining the line splitting patterns in the high resolution H-1 nmr spectra of propylamine, revising the H-1 nmr spectrum of propylamine, proton nmr of propylamine, ppm chemical shifts of the H-1 nmr spectrum of propylamine, explaining and analyzing spin spin line splitting in the H-1 nmr spectrum, how to construct the diagram of the H-1 nmr spectrum of propylamine, how to work out the number of chemically different protons in the structure of the propylamine organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of propylamine using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of propylamine deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of propylamine other names 1-aminopropane n-propylamine 1-propanamine 1-propylamine

Associated links

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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