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Advanced Organic Chemistry: 1H NMR spectrum of 2-methylhexane

The H-1 hydrogen-1 (proton) NMR spectrum of 2-methylhexane

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 2-methylhexane

C7H16 low and high resolution 1H proton nmr spectrum of 2-methylhexane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for 2-methylhexane 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 - 2-methylhexane here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of 2-methylhexane 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 2-methylhexane molecule.

2-methylhexane C7H16 alkanes structure and naming (c) doc b alkanes structure and naming (c) doc b alkanes structure and naming (c) doc b

Interpreting the H-1 NMR spectrum of 2-methylhexane

For relatively simple molecules, the low resolution H-1 NMR spectrum of 2-methylhexane is may or may not be a good starting point (low resolution diagram above).

You can observe three main peaks, but two include resonances that overlap each other.

Theoretically, the hydrogen atoms (protons) of 2-methylhexane occupy 6 different chemical environments so that a very high resolution NMR spectra should show 6 peaks of different H-1 NMR chemical shifts (diagram above for 2-methylhexane).

(CH3)2CHCH2CH2CH2CH3

Note that from the structure of 2-methylhexane and theory the proton ratio in the spectrum should be 6:1:2:2:3 of the 6 colours of the protons in the 6 chemically different environments

Chemical shifts (a) to (f) on the H-1 NMR spectrum diagram for 2-methylhexane.

Although there are 7 hydrogen atoms in the molecule, there are only 6 possible different chemical environments for the hydrogen atoms in 2-methylhexane molecule.

The two 'left-hand' methyl groups include six equivalent protons.

However, because several resonances are close together you seem to observe ...

a ratio of 1:6:9 applied to the proton ratio of the groups 1 x CH : 3 x CH2 : 3 x CH3

The high resolution 1H NMR spectrum of 2-methylhexane

This is problematical because of the close proximity of several of the chemical shifts.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 2-methylhexane - 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 2-methylhexane below.

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

(a) 1H Chemical shift 0.87, resonance for the C(CH3)2 groups of protons

(CH3)2CHCH2CH2CH2CH3

Theoretically this resonance would be split into a 1:1 doublet by the CH proton (n+1 = 2).

Evidence for the presence of a -CH- group in the molecule of 2-methylhexane

(b) 1H Chemical shift 1.52 ppm, resonance for the CH proton

(CH3)2CHCH2CH2CH2CH3

Theoretically this resonance would be split into a nonet by the 2 x CH3 and CH2 protons on either side (n+8 = 9).

(c) 1H Chemical shift 1.17 ppm, resonance for the 1st CH2 group (left to right)

(CH3)2CHCH2CH2CH2CH3

Theoretically this resonance would be split into a 1:3:3:1 quartet by the CH and CH2 protons on either side (n+3 = 4).

(d) 1H Chemical shift 1.27 ppm, resonance for the 2nd CH2 group (left to right)

(CH3)2CHCH2CH2CH2CH3

Theoretically this resonance would also be split into a quintet by the CH2 protons on either side (n+4 = 5).

(e) 1H Chemical shift 1.27 ppm, resonance for the 3rd CH2 group (left to right)

(CH3)2CHCH2CH2CH2CH3

Theoretically this resonance would also be split into a sextet by the CH2 and CH3 protons on either side (n+5 = 6).

(f) 1H Chemical shift 0.89 ppm, resonance for the right-hand end methyl group protons

(CH3)2CHCH2CH2CH2CH3

Theoretically this resonance would be split into a 1:2:1 triplet by the CH2 protons on left (n+2 = 3).


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: C7H16 Interpreting the proton H-1 NMR spectra of 2-methylhexane, low resolution & high resolution proton nmr spectra of 2-methylhexane, H-1 nmr spectrum of 2-methylhexane, understanding the hydrogen-1 nmr spectrum of 2-methylhexane, explaining the line splitting patterns in the high resolution H-1 nmr spectra of 2-methylhexane, revising the H-1 nmr spectrum of 2-methylhexane, proton nmr of 2-methylhexane, ppm chemical shifts of the H-1 nmr spectrum of 2-methylhexane, 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 2-methylhexane, how to work out the number of chemically different protons in the structure of the 2-methylhexane organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 2-methylhexane using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 2-methylhexane deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 2-methylhexane examining the 1H nmr spectrum of  2-methylhexane analysing the 1-H nmr spectrum of 2-methylhexane how do you sketch and interpret the H-1 NMR spectrum of 2-methylhexane interpreting interpretation of the 1H proton NMR spectrum of 2-methylhexane (CH3)2CHCH2CH2CH2CH3


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