Advanced level Organic Chemistry: H-1 NMR spectrum of 2-methylbut-2-ene (2-methyl-2-butene)
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Interpreting the 1H NMR spectrum of 2-methylbut-2-ene (2-methyl-2-butene)

[Author ©  Dr Phil Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy - analysing the 1H NMR spectrum of 2-methylbut-2-ene  [spectra page updated Mar 13th 2026 *]

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 H-1 proton NMR spectroscopy - spectra index

Introductory note on the 1H NMR spectra of 2-methylbut-2-ene

Students and teachers please note my explanation of the proton NMR spectrum of 2-methylbut-2-ene is designed for advanced, but pre-university, chemistry courses.

The chemical shift δ splitting pattern effects for 2-methylbut-2-ene are confined to a proton spin-spin coupling effects analysed using the n+1 rule for adjacent non-equivalent proton fields (n is the number of neighbouring protons in a non-equivalent different chemical environment for the 2-methylbut-2-ene molecule).

It is assumed that the integrated intensities of the 1H NMR δ chemical shifts give the ratio of the protons in the different non-equivalent chemical environments of the 2-methylbut-2-ene molecule.

The most common solvent used for investigating the 1H NMR spectrum of compounds like 2-methylbut-2-ene, is CDCl3 and other deuterated solvents to avoid confusion with a 1H NMR signal, 2D (2H) has a different NMR chemical shift.

C5H10 low and high resolution H-1 proton nmr spectrum of 2-methylbut-2-ene (2-methyl-2-butene) analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 1-H nmr for 2-methylbut-2-ene (2-methyl-2-butene) 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-methylbut-2-ene (2-methyl-2-butene) here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of 2-methylbut-2-ene (2-methyl-2-butene) 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-methylbut-2-ene (2-methyl-2-butene) molecule.

2-methylbut-2-ene C5H10 (CH3)2C=CHCH3 alkenes structure and naming (c) doc b , alkenes structure and naming (c) doc b

The molecular structure and naming of alkenes

Interpreting the H-1 NMR spectrum of 2-methylbut-2-ene (2-methyl-2-butene)

For relatively simple molecules, the low resolution H-1 NMR spectrum of 2-methylbut-2-ene (2-methyl-2-butene) is usually a good starting point (low resolution diagram above), but not in this case

All the methyl proton groups have a similar H-1 chemical shift.

The hydrogen atoms (protons) of 2-methylbut-2-ene (2-methyl-2-butene) occupy 4 (not 3) different chemical environments in a very high resolution NMR spectra showing 5 peaks of different H-1 NMR chemical shifts.

CH3C(CH3)=CHCH3

Note the proton ratio 3:3:1:3 of the four colours of the protons in the four chemically different environments

Although there are 10 hydrogen atoms in the molecule, there are 4 possible different chemical environments for the hydrogen atoms in 2-methylbut-2-ene (2-methyl-2-butene) molecule.

The integrated signal proton ratio 3:3:1:3 observed at very high resolution, corresponds with the structural formula of 2-methylbut-2-ene, as 'coloured' in the molecule above.

The high resolution H-1 NMR spectrum of 2-methylbut-2-ene (2-methyl-2-butene)

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 2-methylbut-2-ene (2-methyl-2-butene) - 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-methylbut-2-ene (2-methyl-2-butene) below.

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

(a) 1H Chemical shift 1.68 ppm  CH3C(CH3)=CHCH3

The 'blue' methyl proton resonance should be a singlet, with no adjacent protons on the neighbouring carbon atom.

(b) 1H Chemical shift 1.56 ppm  CH3C(CH3)=CHCH3

The 'brown' methyl proton resonance will be split into a 1:1 doublet by the single 'green' CH proton (n+1 = 2).

Evidence for the presence of a CH group in the molecule of 2-methylbut-2-ene (2-methyl-2-butene)

(c) 1H Chemical shift 1.60 ppm  CH3C(CH3)=CHCH3

The 'purple' methyl proton resonance should be a singlet, with no protons on the neighbouring carbon atom.

Note that (a) and (c) for the =CH2 groups of protons are NOT identical chemical shifts because of the asymmetry of the 2-methylbut-2-ene molecule..

(d) 1H Chemical shift 5.19 for the CH proton CH3C(CH3)=CHCH3

The 'green' CH proton resonance is split into a 1:3:3:1 quartet by the 'brown' methyl protons (n+1 = 4).

Evidence for the presence of a CH3 group in the molecule of 2-methylbut-2-ene (2-methyl-2-butene)

Note that 2-methylbut-2-ene does NOT exhibit E/Z isomerism (cis/tans) because two of the groups on one of the carbon atoms of the double bond are identical.

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

CH3C(CH3)=CHCH3

However, despite this, there are small differences in the field experienced by the protons of the two methyl groups attached to the 'left' carbon of the C=C bond, because there is a difference in their 1H chemical shifts (1.68 and 1.60 ppm).

This must be due to the asymmetry of the groups (H and methyl) attached to the 'right-hand' carbon atom of the C=C double bond.

Note that in some texts chemical shifts (a) and (c) may be shown as one at ~1.65 ppm, they are very close together and require high resolution spectra.

(see further discussion below)

Summary of key points for the H-1 NMR spectrum of 2-methylbut-2-ene plus extra exam revision comments

A structured breakdown of the ¹H NMR spectrum of 2-methylbut-2-ene (C5H10), tailored for advanced A-level chemistry revision. This includes chemical shifts, proton environments, integration ratios, misconceptions, and exam tips aligned with major exam boards.

Key Structural Features relevant for the 1H NMR spectrum of 2-methylbut-2-ene

  • Alkene: Internal C=C double bond
  • Methyl groups: Two attached to the double bond
  • Alkyl chain: One methyl and one methylene group on the opposite side

Chemical Shifts and Proton Environments the 1H NMR spectrum of 2-methylbut-2-ene

Chemical Shift (δ, ppm) Proton Type Environment Description Integration Ratio
~4.7, 5.19 ppm Vinylic H Proton attached directly to C=C (CH=C(CH3)–) 1
~1.7, ~1.65 ppm Allylic CH3 2 methyl groups attached to the C1 of the C=C bond 6 (assuming two equivalent CH3 groups)
~1.0, 1.56 ppm Terminal CH3 Methyl group at end of alkyl chain 3

Total protons: 10
Simplified ratio: 6 : 1 : 3 (for low resolution)

CH3C(CH3)=CHCH3

Unfortunately there is subtle difference between the two terminal methyl groups that really tests students' chemical intuition. It’s easy to overlook in introductory contexts where symmetry is assumed a bit too liberally.

So, in reality, for the 1H NMR Spectrum of 2-methylbut-2-ene there are 4 distinct signals

  • One vinylic protons (=CH-CH3): Each in a slightly different chemical environment due to substitution asymmetry.
  • One methyl group attached to the quaternary carbon (–C(CH3)=): Distinct.
  • Two terminal methyls (–CH3): Appear slightly different because they’re not identical in spatial relation—likely due to restricted rotation or influence from different neighboring groups (in this case both) - they experience slightly different chemical environments.
  • So, for high resolution, the proton ratios are 3 : 3 : 1 : 3

    CH3C(CH3)=CHCH3

Common Misconceptions about the 1H NMR Spectrum of 2-methylbut-2-ene

Misconception Clarification
All methyl groups give the same chemical shift Position relative to C=C affects shielding and shift
Vinylic protons always appear downfield (>6 ppm) Internal alkenes with electron-donating groups may appear around 4.5–5 ppm
Integration values are absolute proton counts They reflect relative numbers — always simplify to the smallest whole ratio
Splitting always occurs Equivalent protons and lack of adjacent non-equivalent Hs can result in singlets

Exam Revision Tips for questions involving the 1H NMR Spectrum of 2-methylbut-2-ene (AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB)

What to Focus On:

  • Chemical shift ranges: Know typical δ values for alkene, methyl, and allylic protons.
  • Integration ratios: Use them to deduce the number of equivalent protons.
  • Symmetry: Recognise equivalent environments to reduce peak count.
  • Peak count: Expect three/four distinct signals for 2-methylbut-2-ene (depends on resolution of given spectra).

Exam-Style Strategy:

  • Step 1: Count peaks — expect 3 due to symmetry.
  • Step 2: Use integration to assign proton counts.
  • Step 3: Match δ values to environments using data sheet.
  • Step 4: Confirm structure by comparing predicted and observed spectrum.

The splitting pattern from proton spin-spin coupling effects is analysed using the n+1 rule for adjacent non-equivalent proton fields (n is the number of neighbouring protons in a non-equivalent different chemical environment) and applied to the 1H NMR spectrum of 2-methylbut-2-ene.
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

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The infrared spectrum of 2-methylbut-2-ene

The mass spectrum of 2-methylbut-2-ene

The C-13 NMR spectrum of 2-methylbut-2-ene

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