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

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

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-chlorobutane

See also Comparing infrared, mass, 1H NMR & 13C NMR spectra of the 4 structural isomers of C4H9Cl

C4H9Cl CH3CHClCH2CH3 low and high resolution 1H proton nmr spectrum of 2-chlorobutane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for sec-butyl chloride 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-chlorobutane here.

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

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For more see Molecular structure, classification and naming of halogenoalkanes (haloalkanes)

Interpreting the H-1 NMR spectrum of 2-chlorobutane

In terms of spin-spin coupling from the possible proton magnetic orientations, for 2-chlorobutane I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH3.

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

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

CH3CHClCH2CH3

Note the proton ratio 3:1:2:3 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-chlorobutane.

Although there are 9 hydrogen atoms in the molecule, there are only 4 possible different chemical environments for the hydrogen atoms in 2-chlorobutane molecule.

The integrated signal proton ratio 3:1:2:3 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 2-chlorobutane.

The high resolution 1H NMR spectrum of 2-chlorobutane

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

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

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

(a) 1H Chemical shift 1.50 ppm, CH3 protons: CH3CHClCH2CH3

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

Evidence for the presence of a CH3 group in the molecule of 2-chlorobutane

(b) 1H Chemical shift 3.97 ppm, CH proton :  CH3CHClCH2CH3

This 1H resonance is split by the adjacent CH3 and CH2 protons into a 1:5:10:10:5:1 sextet (n+1 = 6).

Evidence for the presence of a CH3-C-CH2 grouping in the molecule of 2-chlorobutane

(c) 1H Chemical shift 1.71 ppm, CH2 protons : CH3CHClCH2CH3

This 1H resonance is split by the adjacent CH3 and CH protons into a 1:4:6:4:1 sextet (n+1 = 6).

Evidence for the presence of a CH3-C-CH group in the molecule of 2-chlorobutane

(d) 1H Chemical shift 1.02 ppm, CH3 protons : CH3CHClCH2CH3

This 1H resonance is split by the adjacent CH2 protons into a 1:2:1 triplet (n+1 = 3).

Evidence for the presence of a CH2 group in the molecule of 2-chlorobutane

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

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 4 halogenoalkane isomers of C4H9Cl

NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane and 2-chloro-2-methylpropane image sizes.  These four molecules are structural isomers of molecular formula C4H9Cl and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower aliphatic halogenoalkanes (haloalkanes, alkyl halides, chloroalkanes, alkyl chlorides).

INFRARED SPECTRA (above): Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, there are no other great striking differences, but each could be identified from its infrared spectrum. The infrared spectrum of 2-chloro-2-methylpropane is noticeably simpler in the fingerprint region, perhaps due to the greater symmetry of the molecule.

MASS SPECTRA (above): Theoretically, all four can give the parent molecular ions of m/z 92 and 94, but they are all relatively tiny peaks. 2-chlorobutane and 2-chloro-2-methylpropane give a base ion peak of m/z 57. The base ion peak for 1-chlorobutane is m/z 56 and that of 1-chloro-2-methylpropane is m/z 43. Each gives different patterns of pairs of m/z values two mass units apart, in the peak height ratio of 3:1, if the positive fragment contains a chlorine atom (35Cl or 37Cl) e.g look for m/z pairs 49/51, 63/65 and 77/79 in their mass spectra.

1H NMR SPECTRA (above): The 1H NMR spectra of all four molecules give different integrated proton ratios i.e.1-chlorobutane four peaks of ratio 3:2:2:2; 2-chlorobutane four peaks of ratio 3:3:2:1, 1-chloro-2-methylpropane three peaks of ratio 6:2:1 and 2-chloro-2-methylpropane gives just one peak '1' (effectively no ratio involved), so all four molecular structures can be distinguished from each other by their 1H NMR spectra proton ratios, numbers of peaks and (n+1) rule splitting patterns.

13C NMR SPECTRA (above): The 13C NMR spectra of the four molecules show various numbers of carbon-13 chemical environments i.e 1-chlorobutane and 2-chlorobutane show four 13C NMR resonances, 1-chloro-2-methylpropane three 13C NMR resonances and 2-chloro-2-methylpropane only two 13C resonances (3 and 2 chemical environments respectively. Therefore 1-chloro-2-methylpropane and 2-chloro-2-methylpropane can be distinguished from the other three by their number of resonances in their 13C NMR spectra, but 1-chlorobutane and 2-chlorobutane cannot be distinguished from each other from their number of 13C NMR resonance lines - other data would be required.

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: C4H9Cl CH3CHClCH2CH3 Interpreting the proton H-1 NMR spectra of 2-chlorobutane, low resolution & high resolution proton nmr spectra of 2-chlorobutane, H-1 nmr spectrum of 2-chlorobutane, understanding the hydrogen-1 nmr spectrum of 2-chlorobutane, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of 2-chlorobutane, revising the H-1 nmr spectrum of 2-chlorobutane, proton nmr of 2-chlorobutane, ppm chemical shifts of the H-1 nmr spectrum of 2-chlorobutane, 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-chlorobutane, how to work out the number of chemically different protons in the structure of the 2-chlorobutane organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 2-chlorobutane using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 2-chlorobutane deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 2-chlorobutane examining the 1H nmr spectrum of  2-chlorobutane analysing the 1-H nmr spectrum of 2-chlorobutane how do you sketch and interpret the H-1 NMR spectrum of 2-chlorobutane interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of 2-chlorobutane  assignment of chemical shifts in the proton 1H NMR spectrum of 2-chlorobutane formula explaining spin-spin coupling for line splitting of sec-butyl chloride

Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of 2-chlorobutane. The proton ratio in the 1H NMR spectrum of 2-chlorobutane. Deducing the number of different chemical environments of the protons in the 2-chlorobutane molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of 2-chlorobutane. Analysing the high resolution 1H NMR spectrum of 2-chlorobutane. Analysing the low resolution 1H NMR spectrum of 2-chlorobutane. You may need to know the relative molecular mass of 2-chlorobutane to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of 2-chlorobutane. Revision notes on the proton NMR spectrum of 2-chlorobutane. Matching and deducing the structure of the 2-chlorobutane molecule from its hydrogen-1 NMR spectrum. Proton NMR spectroscopy of  aliphatic halogenoalkanes haloalkanes alkyl halides alkyl chlorides chloroalkanes, 1H NMR spectra of 2-chlorobutane, an isomer of molecular formula C4H9Cl


Links associated with 2-chlorobutane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The infrared spectrum of 2-chlorobutane (sec-butyl chloride)

The mass spectrum of 2-chlorobutane (sec-butyl chloride)

The C-13 NMR spectrum of 2-chlorobutane (sec-butyl chloride)

H-1 proton NMR spectroscopy index  (Please read 8 points at the top of the 1H NMR index page)

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