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Advanced Organic Chemistry: 1H NMR spectrum of 2,4-dimethylpentane

The H-1 hydrogen-1 (proton) NMR spectrum of 2,4-dimethylpentane

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 2,4-dimethylpentane

C7H16 low and high resolution 1H proton nmr spectrum of 2,4-dimethylpentane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for 2,4-dimethylpentane 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 - 2,4-dimethylpentane here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of 2,4-dimethylpentane 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 2,4-dimethylpentane molecule.

2,4-dimethylpentane 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 2,4-dimethylpentane

For relatively simple molecules, the low resolution H-1 NMR spectrum of 2,4-dimethylpentane is a good starting point (low resolution diagram above).

At low resolution you observe an integrated proton ratio of (2) : (2) : (12)

Theoretically, the 16 hydrogen atoms (protons) of 2,4-dimethylpentane occupy 3 different chemical environments so that the low or high resolution NMR spectra should show 3 principal peaks of different H-1 NMR chemical shifts (diagram above for 2,4-dimethylpentane).

(CH3)2CHCH2CH(CH3)2

Note the proton ratio 12:2:2 of the three colours of the protons in the three chemically different environments

Chemical shifts (a) to (c) on the H-1 NMR spectrum diagram for 2,4-dimethylpentane.

Although there are 16 hydrogen atoms in the molecule, there are only 3 possible different chemical environments for the hydrogen atoms in 2,4-dimethylpentane molecule.

The integrated signal proton ratio 6:1:1 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 2,4-dimethylpentane.

The high resolution 1H NMR spectrum of 2,4-dimethylpentane

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 2,4-dimethylpentane - 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 2,4-dimethylpentane below.

So, using the chemical shifts and applying the n+1 rule to 2,4-dimethylpentane and make some predictions using some colour coding! (In problem solving you work the other way round!)

(a) 1H Chemical shift 0.85 ppm, CH3 protons : (CH3)2CHCH2CH(CH3)2

The CH3 proton resonance line is split into a doublet by the adjacent CH proton (n+1 = 2)

Evidence for the presence of a CH group in the molecule of 2,4-dimethylpentane

(b) 1H Chemical shift 1.62 ppm, CH protons: (CH3)2CHCH2CH(CH3)2

The CH proton resonance line is split into a nonet by the adjacent 2 x CH3 and CH2 protons (n+8 = 1)

Evidence for the presence of a (CH3)2-C-CH2 grouping in the molecule of 2,4-dimethylpentane

(c) 1H Chemical shift 1.03 ppm, CH2 protons : (CH3)2CHCH2CH(CH3)2

The CH2 proton resonance line is split into a 1:2:1 triplet by the two adjacent CH protons (n+1 = 3).

Evidence for the presence of a CH-C-CH grouping in the molecule of 2,4-dimethylpentane


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 2,4-dimethylpentane, low resolution & high resolution proton nmr spectra of 2,4-dimethylpentane, H-1 nmr spectrum of 2,4-dimethylpentane, understanding the hydrogen-1 nmr spectrum of 2,4-dimethylpentane, explaining the line splitting patterns in the high resolution H-1 nmr spectra of 2,4-dimethylpentane, revising the H-1 nmr spectrum of 2,4-dimethylpentane, proton nmr of 2,4-dimethylpentane, ppm chemical shifts of the H-1 nmr spectrum of 2,4-dimethylpentane, 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 2,4-dimethylpentane, how to work out the number of chemically different protons in the structure of the 2,4-dimethylpentane organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 2,4-dimethylpentane using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 2,4-dimethylpentane deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 2,4-dimethylpentane examining the 1H nmr spectrum of  2,4-dimethylpentane analysing the 1-H nmr spectrum of 2,4-dimethylpentane how do you sketch and interpret the H-1 NMR spectrum of 2,4-dimethylpentane interpreting interpretation of the 1H proton NMR spectrum of 2,4-dimethylpentane (CH3)2CHCH2CH(CH3)2 


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