propan-2-ol low high resolution H-1 proton nmr spectrum of analysis interpretation of chemical shifts ppm spin spin line splitting H1 2-propanol 1-H nmr doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: H-1 NMR spectrum of propan-2-ol CH₃CH(OH)CH₃

HOME PAGE * SEARCH * GCSE Level Chemistry age ~14-16 * Advanced Level Chemistry age ~16-19

Interpreting and explaining the 1H NMR spectrum of propan-2-ol CH₃CH(OH)CH₃

[Author © Dr Phil Brown GRIC, 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 propan-2-ol [spectra page updated RE-EDIT]

Email doc brown re-edit 1H NMR spectrum of CH₃CHOHCH₃

This is a BIG chemistry website, PLEASE take time to explore it

H-1 proton NMR spectroscopy - spectra index * A couple of basic practise questions

Links associated with propan-2-ol * [privacy policy, cookies and disclaimer]

Introductory note on the 1H NMR spectra of propan-2-ol (2-propanol)

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

The chemical shift δ splitting pattern effects for propan-2-ol 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 propan-2-ol 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 propan-2-ol molecule.

The most common solvent used for investigating the 1H NMR spectrum of compounds like propan-2-ol, 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 propan-2-ol analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 1-H nmr for 2-propanol 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 - propan-2-ol here.

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

Propan-2-ol C₃H₈O, , , , secondary alcohol

The molecular structure and naming of aliphatic alcohols and ethers

Interpreting the H-1 NMR spectrum of propan-2-ol (2-propanol, isopropyl alcohol)

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

The hydrogen atoms (protons) of propan-2-ol occupy 3 different chemical environments so that the low resolution NMR spectra should show three ¹H peaks of different H-1 NMR chemical shifts (diagram above for propan-2-ol).

(CH₃)₂CHOH or CH₃CH(OH)CH₃

Note the integrated proton ratio of 6:1:1 of the 3 colours of the protons in the 3 chemically different environments in the propan-2-ol molecule.

Although there are 8 hydrogen atoms in the molecule, there only 3 possible chemical environments for the hydrogen atoms in propan-2-ol molecule.

The proton ratio of 6:1:1 observed in the 1H NMR spectrum, corresponds with the structural formula of propan-2-ol.

The high resolution spectrum of propan-2-ol

All low and high resolution spectra of propan-2-ol show 3 groups of protons and in the ratio expected from the formula of propan-2-ol.

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

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

(a) Chemical shift 1.20 ppm the two CH₃ groups of protons (6 equivalent protons)

The single CH proton splits the CH₃ resonance into a 1:1 doublet (n+1 = 2).

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

(b) Chemical shift 4.01 ppm the lone CH proton (1 proton)

The single CH proton is split by the 6 methyl protons into a 1:6:15:20:15:6:1 septet (n+1 = 7), in terms of the relative intensities of the H-1 NMR resonance lines.

Evidence for the presence a CH₃-CH_x-CH₃ grouping in the molecule of propan-2-ol (x = 2 or 1 as in the case of propan-2-ol).

(c) Chemical shift 2.16 ppm the lone OH proton (1 proton)

Generally speaking, unless ultra dry and very high resolution, the hydroxyl proton resonance is not split and neither does it cause a splitting effect itself (see note at end).

Therefore you see a singlet resonance.

Note on the OH proton resonance

If the alcohol is impure, containing water or any source of labile protons, because water and the alcohol exchange protons e.g.

R-O-H + H-O-H R-O-H + H-O-H

This means the CH₂ protons no longer experience a 'simple' local field from one singlet proton from two possible orientations, but, over a finite period, experience the averaging effect of exchanging protons.

This removes the spin - spin coupling effect and the OH proton resonance just shows up as a singlet if the butan-1-ol contains even a trace of water (or acid).

This sort of exchange cannot happen with the alkyl protons, but is common with molecules containing a hydroxyl (OH) hydrogen atom like alcohols and carboxylic acids.

Not only that, you also get proton transfer between the alcohol molecules i.e.

R-O-H + H-O-R R-O-H + H-O-R

which gives the same effect as traces of water of acid.

So, in propan-2-ol, all you usually see in the H-1 NMR spectrum is the mutual splitting of the CH and CH₃ proton resonances plus a singlet line for the OH proton resonance.

EXTRA NOTE on why the OH proton chemical shift is usually observed as a singlet in alcohols like propan-2-ol and how deuterium oxide can be used to identify the peak caused by the hydroxyl proton

Although extremely weak acids, there is constant exchanging of protons between alcohol molecules (R = alkyl groups of propan-2-ol).

R-O-H + H-O-R R-O-H + H-O-R

The rate of proton transfer is increased by traces of water.

R-O-H + H-O-H R-O-H + H-O-H

This cannot happen with the non-acidic C-H protons of alkyl groups in alcohols like propan-2-ol.

This rapid proton transfer interferes with the field splitting effects of the hydroxyl O-H protons and carbon C-H protons and the spin-spin coupling effects disappear.

This phenomena can be used to identify the O-H proton resonance from other C-H proton resonances in hydroxyl molecules like propan-2-ol.

If deuterium oxide (D₂O, where D = ²H) is added to the NMR sample, the ¹H protons are rapidly replaced by ²H protons in the propan-2-ol molecule.

R-O-H + D-O-D R-O-D + H-O-D

The ²H chemical shift frequency is different to the ¹H chemical shift frequency, so the effect of D₂O is to remove the chemical shift for the OH proton from the ¹H NMR spectrum of propan-2-ol, thereby identifying the original ¹H chemical shift as belonging to the hydroxyl group O-H proton and not a C-H proton of the propan-2-ol molecule.

Questions

Some basic practice exam questions based on the 1H NMR spectrum of propan-2-ol.

Jot down your responses and check out the answers

Answer with as much reasoning as possible.

ANSWERS

If you think there are any errors, please email me asap at chem55555@hotmail.com

I don't mind if students/teachers do a selected printout of these questions and answers.

Q1 How many principal 1H NMR chemical shifts would you expect for propan-2-ol?

Q2 How would the ¹H NMR spectrum of the C₃H₈O isomers propan-1-ol and methoxyethane compare with propan-2-ol?

Q3 What would be the effect of adding D₂O to a sample of propan-2-ol and a sample of methoxyethane in terms of the 1H NMR spectrum investigation?

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 isomers of C₃H₈O 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 propan-1-ol, propan-2-ol and methoxyethane image sizes.

	I wasn't able to obtain an infrared spectrum for methoxyethane, so I've added the infrared spectrum of ethoxyethane to enable a few comparisons with two aliphatic alcohols Comparing the infrared spectra of propan-1-ol, propan-2-ol and methoxyethane Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C₃H₈O Propan-1-ol, propan-2-ol and methoxyethane exemplify infrared spectra of the lower members of the homologous series of aliphatic alcohols and ethers
INFRARED SPECTRA (above): There are, as expected, differences in the fingerprint region at wavenumbers 1500 to 400 cm^-1, but most absorptions for all three molecules are the various C-O and the many C-H vibrational modes. However, there is one characteristic distinguishing absorption only present in the infrared spectra of alcohols, but not in ethers, that is the broad O-H stretching vibration peaking at ~3350 cm^-1. There is also another broad absorption band (origin?) peaking at ~650 cm^-1 in the alcohol spectra, but not in the ether spectra.

	Comparing the mass spectra of propan-1-ol, propan-2-ol and methoxyethane Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C₃H₈O Propan-1-ol, propan-2-ol and methoxyethane exemplify the mass spectra of the lower members of the homologous series of aliphatic alcohols and ethers
MASS SPECTRA (above): The base ion peaks are m/z 45 for propan-2-ol and methoxyethane, but that of propan-1-ol is m/z 31. Many of the fragmentation ions are common to all three spectra. The m/z 45 ion is peak is much smaller in the propan-1-ol spectrum compared to the other two.

	Comparing the 1H proton NMR spectra of propan-1-ol, propan-2-ol and methoxyethane Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C₃H₈O Propan-1-ol, propan-2-ol and methoxyethane exemplify the 1H proton NMR spectra of the lower members of the homologous series of aliphatic alcohols and ethers
1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different integrated proton ratios for the different ¹H chemical environments i.e. the proton ratios are as follows: propan-1-ol 3:2:2:1; propan-2-ol 6:1:1 and methoxyethane 3:2:3. Therefore, all three can be distinguished by their ¹H NMR spectra.

	Comparing the carbon-13 NMR spectra of propan-1-ol, propan-2-ol and methoxyethane Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C₃H₈O Propan-1-ol, propan-2-ol and methoxyethane exemplify the carbon-13 NMR spectra of members of the lower members of the homologous series of aliphatic alcohols and ethers
13C NMR SPECTRA (above): The ¹³C NMR spectra of propan-1-ol and methoxyethane show three different ¹³C NMR chemical shifts, but propan-2-ol can be distinguished from the other two by exhibiting only two chemical shift lines. You would need other spectral data to distinguish propan-1-ol and methoxyethane.

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 propan-2-ol.

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: 2-propanol isopropyl alcohol Interpreting the proton H-1 NMR spectra of propan-2-ol, low resolution & high resolution proton nmr spectra of propan-2-ol, H-1 nmr spectrum of propan-2-ol, understanding the hydrogen-1 nmr spectrum of propan-2-ol, explaining the line splitting patterns in the high resolution H-1 nmr spectra of propan-2-ol, revising the H-1 nmr spectrum of propan-2-ol, proton nmr of propan-2-ol, ppm chemical shifts of the H-1 nmr spectrum of propan-2-ol, 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 propan-2-ol, how to work out the number of chemically different protons in the structure of the propan-2-ol organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of propan-2-ol using the n+1 rule to explain the spin - spin coupling NMR splitting in the proton nmr spectrum of propan-2-ol deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of propan-2-ol examining the 1H nmr spectrum of propan-2-ol analysing the 1-H nmr spectrum of propan-2-ol how do you sketch and interpret the H-1 NMR spectrum of propan-2-ol 2-propanol isopropyl alcohol isomer of molecular formula C3H8O Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of propan-2-ol 2-propanol. The proton ratio in the 1H NMR spectrum of propan-2-ol 2-propanol. Deducing the number of different chemical environments of the protons in the propan-2-ol 2-propanol molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of propan-2-ol 2-propanol. Analysing the high resolution 1H NMR spectrum of propan-2-ol 2-propanol. Analysing the low resolution 1H NMR spectrum of propan-2-ol 2-propanol. You may need to know the relative molecular mass of propan-2-ol 2-propanol to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of propan-2-ol 2-propanol. Revision notes on the proton NMR spectrum of propan-2-ol 2-propanol. Matching and deducing the structure of the propan-2-ol 2-propanol molecule from its hydrogen-1 NMR spectrum. Proton NMR spectroscopy of aliphatic alcohols, 1H NMR spectra of propan-2-ol 2-propanol, an isomer of molecular formula C3H8O Explanatory diagram of the 1H H-1 proton NMR spectrum of the propan-2-ol 2-propanol molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of propan-2-ol 2-propanol. How to explain the H-1 NMR spectrum of propan-2-ol 2-propanol. The values of the integrated proton ratios in the 1-H NMR spectrum of the propan-2-ol 2-propanol molecule. How to work out the molecular structure of the propan-2-ol 2-propanol molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the propan-2-ol 2-propanol molecule explained. What does the H-1 proton NMR spectrum tell us about the structure and properties of the propan-2-ol 2-propanol molecule? How do you interpret the H-1 NMR spectrum of propan-2-ol How to interpret the H-1 NMR spectrum of propan-2-ol Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the propan-2-ol molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of propan-2-ol. How to explain the H-1 NMR spectrum of propan-2-ol. The chemical shifts and integrated values of the proton ratios in the 1-H NMR spectrum of the propan-2-ol molecule. How to work out the molecular structure of the propan-2-ol molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the propan-2-ol molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the propan-2-ol molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of propan-2-ol. 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 propan-2-ol

Links associated with propan-2-ol

The chemistry of ALCOHOLS revision notes INDEX

The infrared spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

The mass spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

The C-13 NMR spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

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

Index of my advanced (pre-college/university) organic chemistry revision notes

Index of all my spectroscopy pages

Index of all my isomerism pages

The chemistry of alkanes and the petrochemical industry

The chemistry of alkenes

The chemistry of haloalkanes

The chemistry of alcohols

The chemistry of aldehydes and ketones

The chemistry of carboxylic acids and derivatives

The chemistry of organo-nitrogen compounds

The chemistry of aromatic compounds

ANSWERS to the practice exam questions based on the 1H NMR spectrum of propan-2-ol.

Q1 How many principal 1H NMR chemical shifts would you expect for propan-2-ol?

ANSWER: Three different ¹H proton chemical environments, CH₃CH(OH)CH₃

Q2 How would the ¹H NMR spectrum of the C₃H₈O isomers propan-1-ol and methoxyethane compare with propan-2-ol?

ANSWER: CH₃CH₂CH₂OH would show four principal 1H NMR chemical shifts and CH₃OCH₂CH₃ three.

Q3 What would be the effect of adding D₂O to a sample of propan-2-ol and a sample of methoxyethane in terms of the NMR spectrum investigation?

ANSWER: The OH chemical shift would be reduced for propan-2-ol because of rapid proton exchange

ROH + D-O-D ROD + D-O-H, 2D has a different proton resonance.

but has no effect on methoxyethane's 1H NMR spectrum, no OH to undergo proton exchange.

For more information see Isomers of molecular formula C₃H₈O (M_r = 60)

The H-1 NMR spectrum of Propan-1-ol

and The H-1 NMR spectrum of methoxyethane

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on spectroscopy are suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE advanced level chemistry, CCEA advanced level chemistry, US grade 11-12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.