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Advanced Organic Chemistry: H-1 NMR spectrum of butanone

The H-1 hydrogen-1 (proton) NMR spectrum of butanone

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB 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 butanone (2-butanone, butan-2-one)

low and high resolution H-1 proton nmr spectrum of butanone analysis interpretation of chemical shifts ppm spin spin line splitting diagram for  2-butanone butan-2-one 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 - butanone here.

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

Butanone C4H8O,  aldehydes and ketones nomenclature (c) doc b , aldehydes and ketones nomenclature (c) doc b , aldehydes and ketones nomenclature (c) doc b , aldehydes and ketones nomenclature (c) doc b

Interpreting the H-1 NMR spectrum of butanone

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

The hydrogen atoms (protons) of butanone occupy 3 different chemical environments so that the H-1 proton low resolution NMR spectra should show 3 peaks (diagram above for butanone).

CH3COCH2CH3

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

Although there are 8 hydrogen atoms in the molecule, there only 3 possible chemical environment for the hydrogen atoms.

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

The high resolution spectrum of butanone

So, using the chemical shifts and applying the n+1 rule to CH3COCH2CH3:

The chemical shift at 2.16 ppm is for the 'left' methyl group and no splitting is evident because there s no adjacent proton on a the carbonyl (C=O) carbon atom.

The CH2 protons are split into a 1:3:3:1 quartet by the 'right-hand' CH3 group at 2.45 ppm - evidence of a CH3 group in the molecule.

The 'right-hand' CH3 protons are split into a 1:2:1 triplet by the CH2 group at 1.06 ppm - evidence of a CH2 group in the molecule.

Note that the 'real spectra' intensity ratios e.g. 1:2:1 and 1:3:3:1 are not perfect, but do look something like the theory predicts for butanone!

 


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 butanone 2-butanone butan-2-one, low resolution & high resolution proton nmr spectra of butanone, H-1 nmr spectrum of butanone, understanding the hydrogen-1 nmr spectrum of butanone, explaining the line splitting patterns in the high resolution H-1 nmr spectra of butanone, revising the H-1 nmr spectrum of butanone, proton nmr of butanone, ppm chemical shifts of the H-1 nmr spectrum of butanone, 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 butanone, how to work out the number of chemically different protons in the structure of the butanone organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of butanone 2-butanone butan-2-one


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