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Advanced Organic Chemistry: 1H NMR spectrum of 2-methylpropan-1-ol

Interpreting the 1H NMR spectrum of 2-methylpropan-1-ol (isobutyl alcohol)

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-methylpropan-1-ol

low/high resolution 1H proton nmr spectrum of 2-methylpropan-1-ol C4H10O (CH3)2CHCH2OH analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for isobutyl alcohol 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 - 2-methylpropan-1-ol here.

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

2-methylpropan-1-ol   C4H10O   alcohols and ether structure and naming (c) doc b    alcohols and ether structure and naming (c) doc b    alcohols and ether structure and naming (c) doc b

Interpreting the H-1 NMR spectrum of 2-methylpropan-1-ol

In terms of spin-spin coupling from the possible proton magnetic orientations, for 2-methylpropan-1-ol I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH2-CH3, -CH-CH3- protons etc. (problems with -OH proton resonance)

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

The hydrogen atoms (protons) of 2-methylpropan-1-ol occupy 4 different chemical environments so that the low resolution NMR spectra should show 4 principal peaks of different H-1 NMR chemical shifts (diagram above for 2-methylpropan-1-ol).

(CH3)2CHCH2OH

Note the proton ratio 6:1:2:1 of the 4 colours of the protons in the 4 chemically different environments

Chemical shifts (a) to (d) on the H-1 NMR spectrum diagram for 2-methylpropan-1-ol.

Although there are 10 hydrogen atoms in the molecule, there are only 4 possible different chemical environments for the hydrogen atoms in 2-methylpropan-1-ol molecule.

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

The high resolution 1H NMR spectrum of 2-methylpropan-1-ol

All low and high resolution spectra of 2-methylpropan-1-ol show 4 groups of proton resonances and in the 4 ratio expected from the formula of 2-methylpropan-1-ol.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 2-methylpropan-1-ol - 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-methylpropan-1-ol below.

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

BUT ...

an important note about the hydroxyl group on 2-methylpropan-2-ol (for pre-university students):

Unless the alcohol is completely free of water (difficult), the hydrogen on the -O-H hydroxyl group and any hydrogens on the adjacent carbon don't interact to produce any spin-spin splitting. Therefore the -OH peak shows up as a singlet and you don't usually have to consider its effect on any hydrogen atoms, if present on the adjacent carbon atom (C-OH), and, neither do you have to consider the splitting effect of adjacent C-H protons on the hydrogen of the OH group.

(a) 1H Chemical shift ppm 0.92 ppm for the methyl protons: (CH3)2CHCH2OH

This 1H resonance is split into a 1:1 doublet by the adjacent CH proton (n+1 = 2).

Evidence for the presence of a CH group in the molecule of 2-methylpropan-1-ol

(b) 1H Chemical shift 1.75 ppm for the CH proton: (CH3)2CHCH2OH

This 1H resonance is split into a nonet by the adjacent CH2 and 2 x CH3 protons (n+8 = 9).

Evidence for the presence of a (CH3)2CHCH2 grouping in the molecule of 2-methylpropan-1-ol

(c) 1H Chemical shift 3.39 ppm for the CH2 protons : (CH3)2CHCH2OH

This 1H resonance is split into a 1:1 doublet by the adjacent CH proton (n+1 = 2).

Evidence for the presence of a CH group in the molecule of 2-methylpropan-1-ol

(d) 1H Chemical shift 2.07 ppm for the hydroxyl proton: (CH3)2CHCH2OH

This proton resonance is not split, and neither does this proton cause field splitting in the CH2 protons.

Note the decreasing effect on the 1H chemical shift as the proton is further from the more electronegative oxygen atom in 2-methylpropan-1-ol.


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: C4H10O (CH3)2CHCH2OH  Interpreting the proton H-1 NMR spectra of 2-methylpropan-1-ol, low resolution & high resolution proton nmr spectra of 2-methylpropan-1-ol, H-1 nmr spectrum of 2-methylpropan-1-ol, understanding the hydrogen-1 nmr spectrum of 2-methylpropan-1-ol, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of 2-methylpropan-1-ol, revising the H-1 nmr spectrum of 2-methylpropan-1-ol, proton nmr of 2-methylpropan-1-ol, ppm chemical shifts of the H-1 nmr spectrum of 2-methylpropan-1-ol, 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-methylpropan-1-ol, how to work out the number of chemically different protons in the structure of the 2-methylpropan-1-ol organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 2-methylpropan-1-ol using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 2-methylpropan-1-ol deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 2-methylpropan-1-ol examining the 1H nmr spectrum of  2-methylpropan-1-ol analysing the 1-H nmr spectrum of 2-methylpropan-1-ol how do you sketch and interpret the H-1 NMR spectrum of 2-methylpropan-1-ol interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of 2-methylpropan-1-ol  assignment of chemical shifts in the proton 1H NMR spectrum of 2-methylpropan-1-ol formula explaining spin-spin coupling for line splitting for isobutyl alcohol


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