pent-1-ene 1-pentene's low high resolution H-1 proton nmr spectrum of pent-1-ene 1-pentene analysis interpretation of chemical shifts ppm spin spin line splitting doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: 1H proton NMR spectrum of Pent-1-ene H₂C=CHCH₂CH₂CH₃

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Interpreting the H-1 (proton) NMR spectrum of Pent-1-ene (1-pentene)

[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 analysis of pent-1-ene [spectra page updated Mar 25th 2026 *]

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H-1 proton NMR spectroscopy - spectra index

Introductory note on the 1H NMR spectra of pent-1-ene

Students and teachers please note my explanation of the proton NMR spectrum of pent-1-ene is designed for advanced, but pre-university, chemistry courses.

The chemical shift δ splitting pattern effects for pent-1-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 pent-1-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 pent-1-ene molecule.

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

low and high resolution H-1 proton nmr spectrum of pent-1-ene 1-pentene analysis interpretation of chemical shifts ppm spin spin line splitting diagram 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 - pent-1-ene here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of pent-1-ene represent the peaks of the intensity of the chemical shifts of pent-1-ene (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 pent-1-ene molecule.

Pent-1-ene, , , (1-pentene)

an alkene The molecular structure and naming of alkenes

Interpreting the H-1 NMR spectrum of Pent-1-ene

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

The hydrogen atoms (protons) of pent-1-ene occupy 5 different chemical environments so that the H-1 proton low resolution NMR spectra should show five ₁H NMR chemical shift peaks, which it does (diagram above).

CH₃CH₂CH₂CH=CH₂

(note the five different colours of the protons in pent-1-ene)

Since all 5 hydrogen atoms in the molecule are in 5 different chemical environments, pent-1-ene will show 5 different chemical shifts in its H-1 NMR spectrum.

The ratio of the area under the NMR 'peaks' should be a proton ratio of 3 : 2 : 2 : 1 : 2 from the molecular structured of pent-1-ene (colour coded above) i.e. the proton ratios in the molecule.

As you can see, the high resolution spectrum of pent-1-ene is complex

(a) Chemical shift 0.91 ppm

CH₃CH₂CH₂CH=CH₂

The end CH₃ group is split into a triplet (1 : 2 : 1 lines at 0.91 ppm) by the adjacent CH₂ group.

(b) The 1.43 ppm chemical shift:

CH₃CH₂CH₂CH=CH₂

From the n+1 rule, the 'left-hand' 1st CH₂ (H₂) protons are split by the CH₃ (H₃) protons and by the 'right-hand' 2nd CH₂ protons (H₂), (5 protons in total), into a 1:5:10:10:5:1 sextet of resonance lines (n+1 = 6).

This is pattern of resonances is a good indication of a propyl group (CH₃CH₂CH₂).

(c) The 2.02 ppm chemical shift:

CH₃CH₂CH₂CH=CH₂

The 'middle' 2nd CH₂ protons (H₂) are split by the left CH₂ protons (H₂) and the =CH proton on the right (H), (3 protons in total), in to a 1:3:3:1 quartet of resonance lines (n+1 = 4).

(d) The 5.81 ppm chemical shift:

CH₃CH₂CH₂CH=CH₂

The CH proton (H) is split by the left CH₂ protons (H₂) and the end =CH₂ protons (H), (4 protons in total), into a 1:4:6:4:1 quintet of resonance lines (n+1 = 5).

(e) Chemical shift 4.97 ppm

CH₃CH₂CH₂CH=CH₂

The end =CH₂ group is split into a doublet (1 : 1 lines at 4.97 ppm) by the adjacent CH= group (n+1 = 2).

The ¹H NMR chemical shifts tend to much higher for protons directly bonded to the carbon atoms of the C=C double bond compared to those not so.

Non of these 'splitting' predictions is clear on the H-1 NMR spectra of pent-1-ene shown on the NMR spectrum diagram above.

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).

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: Interpreting the proton H-1 NMR spectra of pent-1-ene 1-pentene, low resolution & high resolution proton nmr spectra of pent-1-ene 1-pentene, H-1 nmr spectrum of pent-1-ene 1-pentene, understanding the hydrogen-1 nmr spectrum of pent-1-ene 1-pentene, explaining the line splitting patterns in the high resolution H-1 nmr spectra of pent-1-ene 1-pentene, revising the H-1 nmr spectrum of pent-1-ene 1-pentene, proton nmr of pent-1-ene 1-pentene, ppm chemical shifts of the H-1 nmr spectrum of pent-1-ene 1-pentene, 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 pent-1-ene 1-pentene, how to work out the number of chemically different protons in the structure of the pent-1-ene 1-pentene organic molecule How do you interpret the H-1 NMR spectrum of pent-1-ene (1-pentene) How to interpret the H-1 NMR spectrum of pent-1-ene (1-pentene) Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the pent-1-ene (1-pentene) molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of pent-1-ene (1-pentene). How to explain the H-1 NMR spectrum of pent-1-ene (1-pentene). The chemical shifts and integrated values of the proton ratios in the 1-H NMR spectrum of the pent-1-ene (1-pentene) molecule. How to work out the molecular structure of the pent-1-ene (1-pentene) molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the pent-1-ene (1-pentene) molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the pent-1-ene (1-pentene) molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of pent-1-ene (1-pentene). interpretation diagram explaining the proton splitting pattern produced from the n+1 rule and the theoretical ratio of chemical shift δ and values of intensities for the proton NMR spectrum lines of pent-1-ene (1-pentene)

What next? Associated links for pent-1-ene (1-pentene)

The infrared spectrum of pent-1-ene (1-pentene)

The mass spectrum of Pent-1-ene (1-pentene)

The C-13 NMR spectrum of Pent-1-ene (1-pentene)

The chemistry of ALKENES revision notes INDEX

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

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