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Advanced Organic Chemistry: 1H NMR spectrum of dimethylamine

Interpreting the H-1 NMR spectrum of dimethylamine (N-methylmethanamine)

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 dimethylamine

1H proton nmr spectrum of dimethylamine low/high resolution diagrams C2H7N CH3NHCH3 analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for N-methylmethanamine 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 - dimethylamine here.

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

Dimethylamine, N-methylmethanamine, C2H7N, (c) doc b , (c) doc b , (c) doc b

Interpreting the H-1 NMR spectrum of dimethylamine

In terms of spin-spin coupling from the possible proton magnetic orientations, for dimethylamine I have only considered the interactions of non-equivalent protons on adjacent carbon atoms which doesn't apply here, and the N-H proton resonance is not normally split by adjacent C-H protons and neither is the adjacent C-H resonance split by the N-H protons, see note on resonance (b) below.

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

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

CH3NHCH3  or  (CH3)2NH

Note the proton ratio 6:1 of the 2 colours of the ? protons of dimethylamine in the 2 chemically different proton environments

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

Although there are 7 hydrogen atoms in the molecule, there are only 7 possible different chemical environments for the hydrogen atoms in dimethylamine molecule.

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

The high resolution 1H NMR spectrum of dimethylamine

The high resolution spectra of dimethylamine shows 2 groups of proton resonances and in the 6:1 ratio expected from the structural formula of dimethylamine.

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

However, applying the n+1 rule to dimethylamine isn't necessary, both proton resonances

(a) 1H Chemical shift 2.13 ppm, methyl protons: CH3NHCH3

There are no adjacent C-H protons, and the N-H protons do not cause a splitting, so this 1H NMR resonance shows up as a singlet in the dimethylamine spectrum.

(b) 1H Chemical shift ?: CH3NHCH3

The adjacent C-H protons do not cause a splitting, so this 1H NMR resonance shows up as a singlet in the dimethylamine spectrum.

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 (and vice versa) - even a trace of water catalyses this effect.

e.g. for aliphatic primary/secondary aliphatic amines, if R = H or alkyl

R2N-H  +  H-O-H  (c) doc b  H-R2N-H+  +  OH-  (c) doc b  R2N-H  +  H-O-H


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

Key words & phrases: C2H7N CH3NHCH3 (CH3)2NH HN(CH3)2 Interpreting the proton H-1 NMR spectra of dimethylamine, low resolution & high resolution proton nmr spectra of dimethylamine, H-1 nmr spectrum of dimethylamine, understanding the hydrogen-1 nmr spectrum of dimethylamine, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of dimethylamine, revising the H-1 nmr spectrum of dimethylamine, proton nmr of dimethylamine, ppm chemical shifts of the H-1 nmr spectrum of dimethylamine, 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 dimethylamine, how to work out the number of chemically different protons in the structure of the dimethylamine organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of dimethylamine using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of dimethylamine deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of dimethylamine examining the 1H nmr spectrum of  dimethylamine analysing the 1-H nmr spectrum of dimethylamine how do you sketch and interpret the H-1 NMR spectrum of dimethylamine interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of dimethylamine  assignment of chemical shifts in the proton 1H NMR spectrum of dimethylamine formula explaining spin-spin coupling for line splitting for dimethylamine secondary aliphatic amine functional group N-methylmethanamine N-methylmethylamine


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