HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY CHEMISTRY PHYSICS * ADVANCED LEVEL CHEMISTRY

SPECTROSCOPY INDEXES  *  All Advanced Organic Chemistry Notes  *  [SEARCH BOX]

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

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

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-methylbutane

See also comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 alkane isomers of C5H12

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

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

2-methylbutane C5H12 alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b , alkanes structure and naming (c) doc b

For more see The molecular structure and naming of alkanes

Interpreting the H-1 NMR spectrum of 2-methylbutane

For relatively simple molecules, the low resolution H-1 NMR spectrum of 2-methylbutane is a good starting point.

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

(CH3)2CHCH2CH3

Note the integrated proton ratio 6:1:2:3 of the 4 colours of the protons in the 4 chemically different environments

Although there are 12 hydrogen atoms in the molecule, there only 4 possible 1H chemical environments for the hydrogen atoms in 2-methylbutane molecule.

The proton ratio  6:1:2:3 observed, corresponds with the structural formula of 2-methylbutane.

The high resolution spectrum of 2-methylbutane

All low and high resolution spectra of 2-methylbutane show 4 groups of protons and in the ratio expected from the structural formula of 2-methylbutane.

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

So, using the chemical shifts and applying the n+1 rule to 2-methylbutane

(a) Chemical shift 0.869 ppm, the left-hand 2 x CH3 protons,  (CH3)2CHCH2CH3

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

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

(b) Chemical shift 1.45 ppm, the lone CH proton,  (CH3)2CHCH2CH3

This proton resonance is split into a nonet (n+1 = 9 because of 2 x CH3 plus CH2)

Evidence for the presence of a  (CH3)2CHCH2 group in the molecule of 2-methylbutane.

(c) Chemical shift 1.20 ppm, the CH2 protons,  (CH3)2CHCH2CH3

This proton resonance is split into a 1:4:6:4:1 quintet by the CH proton and the right-hand CH3 group protons (n+1 = 5).

(d) Chemical shift 0.865 ppm, the right-hand CH3 protons,  (CH3)2CHCH2CH3

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

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


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
Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 alkane isomers of C5H12

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 pentane, 2-methylbutane and 2,2-dimethylpropane image sizes.

Comparing the infrared spectra of pentane, 2-methylbutane and 2,2-dimethylpropane

Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C5H12

Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify infrared spectra of  the alkane homologous series CnH2n+2  hydrocarbon molecules, where n = 5

INFRARED SPECTRA (above): There are, as expected, differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, but there is no specific infrared absorption band for a functional group. The infrared spectra of pentane and 2-methylbutane seem very similar, but that of 2,2-dimethylpropane seems much simpler.

Comparing the mass spectra of pentane, 2-methylbutane and 2,2-dimethylpropane

Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C5H12

Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify the mass spectra of  the alkane series CnH2n+2  hydrocarbon molecules, where n = 5

MASS SPECTRA (above): All three hydrocarbons show some similarities in their mass spectra e.g. m/z ions 27 to 29 for [C2Hx]+ (x = 2 and 4). The molecular ion peaks will be the same for all three isomers (m/z 72), but it is very tiny for 2,2-dimethypropane. The pattern ratios for m/z 39 to 43 are similar for pentane and 2-methylbutane, but m/z 42 and 43 ions are almost absent from the 2,2-dimethylpropane spectrum. The base peak ion for pentane is m/z 43, but for 2-methylbutane and 2,2-dimethylpropane it is m/z 57.

Comparing the 1H proton NMR spectra of pentane, 2-methylbutane and 2,2-dimethylpropane

Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C5H12

Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify the 1H proton NMR spectra of the alkane homologous series CnH2n+2  hydrocarbon molecules where, n = 5

1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios for the different 1H chemical environments i.e. pentane's proton ratio is 3:2:1 (from 6:4:2 H's in the molecule). 2-methylbutane's proton ratio is 6:1:2:3 and 2,2-dimethylpropane's doesn't have a proton ratio, all hydrogen atoms are equivalent. This means all three isomeric C5H12 hydrocarbons can be distinguished from their 1H NMR spectra.

Comparing the carbon-13 NMR spectra of pentane, 2-methylbutane and 2,2-dimethylpropane

Pentane, 2-methylbutane and 2,2-dimethylpropane are structural isomers of molecular formula C5H12

Pentane, 2-methylbutane and 2,2-dimethylpropane exemplify the carbon-13 NMR spectra of members of  the alkane homologous series CnH2n+2  hydrocarbon molecules, where n = 5

13C NMR SPECTRA (above): The 13C NMR spectra of the three molecules show different numbers of carbon-13 chemical environments i.e different numbers of 13C NMR resonance lines. So, pentane gives three 13C chemical shifts, 2-methylbutane four and 2,2-dimethylpropane two. This means all three isomeric C5H12 hydrocarbons can be distinguished from their 13C NMR spectra.

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

Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of 2-methylbutane. The proton ratio in the 1H NMR spectrum of 2-methylbutane. Deducing the number of different chemical environments of the protons in the 2-methylbutane molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of 2-methylbutane. Analysing the high resolution 1H NMR spectrum of 2-methylbutane. Analysing the low resolution 1H NMR spectrum of 2-methylbutane. You may need to know the relative molecular mass of 2-methylbutane to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of 2-methylbutane. Revision notes on the proton NMR spectrum of 2-methylbutane. Matching and deducing the structure of the 2-methylbutane molecule from its hydrogen-1 NMR spectrum. Proton NMR spectroscopy of aliphatic alkanes, 1H NMR spectra of 2-methylbutane, an isomer of molecular formula C5H12


Links associated with 2-methylbutane

The chemistry of ALKANES revision notes INDEX

The infrared spectrum for 2-methylbutane

The mass spectrum for 2-methylbutane

The C-13 NMR spectrum for 2-methylbutane

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

ALL SPECTROSCOPY INDEXES

All Advanced Organic Chemistry Notes

Use My Google search site box

Email doc b: chem55555@hotmail.com

TOP OF PAGE

 Doc Brown's Chemistry 

*

TOP OF PAGE