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Advanced Organic Chemistry: H-1 NMR spectrum of E-but-2-ene & Z-but-2-ene

The H-1 hydrogen-1 (proton) NMR spectrum of E-but-2-ene and Z-but-2-ene

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses on molecular spectroscopy analysing H-1 NMR spectra of E-but-2-ene, Z-but-2-ene

trans isomer 2-butene H-1 proton nmr spectrum of E-but-2-ene analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 1-H nmr doc brown's advanced organic chemistry revision notes

cis isomer 2-butene H-1 proton nmr spectrum of Z-but-2-ene analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 1-H nmr 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 - E-but-2-ene and Z-but-2-ene here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of E-but-2-ene and Z-but-2-ene 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 E-but-2-ene and Z-but-2-ene molecule.

 alkenes structure and naming (c) doc b, structural formula of but-2-ene alkenes structure and naming (c) doc b , but doesn't show the two different spatial arrangements possible due to a high energy barrier to rotation about the double bond, known as the E/Z stereoisomers

Z-but-2-ene alkenes structure and naming (c) doc b  or  alkenes structure and naming (c) doc b (cis-2-butene, cis-but-2-ene)

 

 E-but-2-ene alkenes structure and naming (c) doc b or  alkenes structure and naming (c) doc b (trans-2-butene, trans-but-2-ene)

for more details and examples of  E/Z isomerism see ...

STEREOISOMERISM general definition, E/Z (geometric/geometrical cis/trans) isomerism

Interpreting the H-1 NMR spectrum of E-but-2-ene and Z-but-2-ene

The hydrogen atoms (protons) of E-but-2-ene and Z-but-2-ene occupy 2 different chemical environments so that the low or high resolution NMR spectra should show 2 peaks of different H-1 NMR chemical shifts (diagrams above for E-but-2-ene and Z-but-2-ene).

CH3CH=CHCH3

Note the ratio 6:2 =  3:1 of the two colours of the protons in the two chemically different environments

Although there are 6 hydrogen atoms in the molecule, there only 2 possible chemical environments for the hydrogen atoms in E-but-2-ene and Z-but-2-ene molecule.

The proton ratio 3:1 observed, corresponds with the structural formula of E-but-2-ene and Z-but-2-ene.

The high resolution H-1 NMR spectrum of E-but-2-ene and Z-but-2-ene

All low and high resolution spectra of E-but-2-ene and Z-but-2-ene show 2 groups of protons and in the ratio expected from the formula of E-but-2-ene and Z-but-2-ene.

alkeneThe ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of E-but-2-ene and Z-but-2-ene - 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 E-but-2-ene and Z-but-2-ene below.

So, using the chemical shifts and applying the n+1 rule to E-but-2-ene and Z-but-2-ene

The CH3 proton NMR chemical shift

alkenes structure and naming (c) doc b For E-but-2-ene it is 1.58 ppm

alkenes structure and naming (c) doc b For Z-but-2-ene it is 1.54 ppm

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

Despite the difference in geometry, the chemical shift for the CH3 protons is very similar, so the chemical environment of the CH3 protons in but-2-ene must be very similar in both isomers.

Evidence for the presence of a CH group in the molecules of E-but-2-ene and Z-but-2-ene

The CH proton NMR chemical shift

alkenes structure and naming (c) doc b For E-but-2-ene it is 5.58 ppm

alkenes structure and naming (c) doc b For Z-but-2-ene it is 5.37 ppm

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

Despite the difference in geometry, the chemical shift for the CH3 protons is very similar, so the chemical environment of the CH proton in but-2-ene must be very similar in both isomers.


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

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


Links associated with E-but-2-ene and Z-but-2-ene

The chemistry of ALKENES revision notes INDEX

H-1 proton NMR spectroscopy index

ALL SPECTROSCOPY INDEXES

STEREOISOMERISM general definition, E/Z (geometric/geometrical cis/trans) isomerism

All Advanced Organic Chemistry Notes

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