Advanced Organic Chemistry: The 1H NMR spectrum of ethanol

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Interpreting and explaining the 1H hydrogen NMR spectrum of ethanol

Sub-index for this page on the 1H spectroscopy of ethanol

(a) Introductory note on the 1H NMR spectra of ethanol

(b) Diagram of the 1H NMR spectrum of ethanol and its molecular structure

(c) Interpreting and explaining the 1H NMR spectrum of ethanol

(d) Very high resolution 1H NMR spectrum of ultra-pure ethanol under the right condition!

(e) Problems with the hydroxy (O-H) resonance in the H-1 NMR of alcohols containing water

(f) Why the OH proton chemical shift is usually observed as a singlet and how deuterium oxide can be used to identify the peak caused by the hydroxyl proton

(g) A historic note about the 1H NMR spectrum of ethanol

(h) Key revision points and practise questions based on the 1H NMR spectrum of ethanol

(i) Comparison of the infrared, mass, 1H NMR and 13C NMR spectra of the 2 isomers of C2H6O

(j) ANSWERS to the multiple choice questions based on the 1H NMR spectrum of ethanol

[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 ethanol [spectra page updated RE-EDIT]

 email doc brown  * Re-edit 1H NMR spectrum of CH3CH2OH (C2H5OH, ethyl alcohol)

 Key points and practice questions

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 H-1 proton NMR spectroscopy - spectra index

(a) Introductory note on the 1H NMR spectra of ethanol

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

The chemical shift δ splitting pattern effects for ethanol 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 ethanol 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 ethanol molecule.

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

(b) Diagram of the 1H NMR spectrum of ethanol and its molecular structure

low and high resolution H-1 proton nmr spectrum of ethanol analysis interpretation of chemical shifts ppm spin spin line splitting diagram for ethyl alcohol doc brown's advanced organic chemistry revision notes

Ethanol C2H6O, alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b aliphatic alcohol

Revision notes on the structure and naming (nomenclature) of aliphatic ALCOHOLS and ETHERS

(c) Interpreting and explaining the 1H NMR spectrum of ethanol

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 - ethanol here.

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

Interpreting the H-1 NMR spectrum of ethanol

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

The hydrogen atoms (protons) of ethanol occupy 3 different chemical environments so that the H-1 proton low resolution NMR spectra should show 3 1H peaks (diagram above).

CH3CH2OH

Note the ratio of the 3 colours for the 3 proton chemical environments in ethanol.

In terms of the H-1 chemical shifts for ethanol (a) to (c) and applying the n+1 rule:

(a) Centred at 1.22 ppm, the CH3 protons are split by the 2 CH2 protons into a 1 : 2 : 1 triplet (n+1 = 3).

(b) Centred at 3.69 ppm, the CH2 protons are split by the 3 CH3 protons into a 1 : 3 : 3 : 1 quartet (n+3 = 4).

(c) The hydroxy proton O-H gives a chemical shift of 2.61 ppm and shows no significant splitting.

 

Normally the O-H proton resonance is not split by adjacent protons and neither does it, in turn, split the resonance of the same adjacent carbon atom protons - see extra notes below.

I have found that the OH 1H NMR signal for ethanol can vary and much further downfield than the diagram above e.g. a chemical shift ~5 ppm.

The integrated NMR proton ratio observed of 3 : 2 : 1, corresponds with the structural formula of ethanol.

See also comparing the IR, mass, 1H NMR and 13C NMR spectra of isomers of C2H6O below.

(d) Very high resolution 1H NMR spectrum of ultra-pure ethanol under the right condition!

With ultra-pure anhydrous ethanol it is possible to observe the splitting effects by, and of, the hydroxyl proton OH - but its a bit tricky in place!

(a) The CH3 protons give a triplet from the CH2 protons- as above (n+1 = 3) - no change.

(b) You might think the CH2 proton resonance might seem to be split into a quintet (n+1 = 5) by the CH3 and OH protons on either side, and not a quartet. Some diagrams I've seen look like this, but this not actually what happens.

In fact the CH2 protons are split by the CH3 protons into a 1:3:3:1 quartet, but this quartet is split into doublets by the single OH proton (n+1 = 2), so a series of 1:3:3:1 doublets, or 1:1:3:3:3:3:1:1 to be a purist, but this is going beyond pre-university level!

(c) As above, the OH resonance would be split into a triplet (n+1 = 3) by the CH2 protons.

(This is university level NMR spectroscopy, so don't worry, concentrate on the basic proton ratio of 3 : 2 : 1 to match the structure of ethanol).

(e) Problems with the hydroxy (O-H) resonance in the H-1 NMR of alcohols containing water

(i) The first important point to make is, that despite the variety of different chemical shifts for the OH proton resonance quoted in data books, textbooks and internet sources, the integration of the NMR resonances always gives the correct proton ratio in the molecule, in this case 3 : 2 : 1 for ethanol CH3CH2OH

(ii) Apart from the O-H group resonance the NMR spectra of most alcohols conform to what would be expected e.g. the triplet and quartet of the spin-spin splitting effects for the alkyl part resonances of the ethanol molecule.

(iii) However, the OH proton NMR resonance for ethanol is typically quoted as ~2.6 ppm (here) and ~5.3 ppm, and some in between too!

BUT, the main difference you find from various sources is not the OH proton chemical shift, but is it a singlet or a triplet?

(iv) The problem arises if the alcohol is impure e.g. containing water or any source of labile protons, because water and the alcohol, ethanol, exchange protons e.g.

CH3CH2OH  +  H-O-H    CH3CH2OH  +  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 ethanol 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.

CH3CH2OH  +  H-O-CH2CH3    CH3CH2OH  +  H-O-CH2CH3

which can give the same effect as traces of water of acid.

Normally the result is the O-H proton resonance is not split by adjacent protons and neither does it, in turn, split the resonance of the same adjacent carbon atom protons - see extra notes below.

(v) So, in ethanol, all you usually see in the H-1 NMR spectrum is the mutual splitting of the CH2 and CH3 proton resonances plus a singlet line for the OH proton resonance.

Note the actual chemical shift for the OH proton resonance of alcohols can depend on the solvent and concentration used in the NMR machine, often CDCl3 - deuterated trichloromethane solvent.

See also comparing the IR, mass, 1H NMR and 13C NMR spectra of isomers of C2H6O below.

(f) why the OH proton chemical shift is usually observed as a singlet in alcohols like ethanol 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 ethanol).

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 ethanol.

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 ethanol.

If deuterium oxide (D2O, where D = 2H) is added to the NMR sample, the 1H protons are rapidly replaced by 2H protons in the ethanol 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 ethanol, thereby identifying the original 1H chemical shift as belonging to the hydroxyl group O-H proton and not a C-H proton of the ethanol molecule.

historic first 1H NMR spectrum of ethanol (ethyl alcohol) from 1951 at Stanford University by J.T. Arnold, S.S. Dharmatti and M.E. Packard(g) A historic note about the 1H NMR spectrum of ethanol

On the right is the first successful 1H proton NMR spectrum from 1951.  The possibility of the splitting pattern illustrated below from a modern NMR scanner was unknown at the time.

This 1951 Nuclear Magnetic Resonance (NMR) spectrum of ethanol was obtained at Stanford University by J.T. Arnold, S.S. Dharmatti and M.E. Packard and was a major breakthrough in chemical analysis

By detecting three distinct peaks, it provided the first experimental proof of the "chemical shift", so demonstrating that NMR could reveal different aspects of a molecular structure.

Because the hydrogen atoms in ethanol are situated in three unique electron densities (chemical environments), these protons precess at slightly different frequencies - now referred to as chemical shifts versus a standard shift of zero.

This discovery showed that NMR could "see" specific molecular structures, ultimately earning Felix Bloch and Edward Purcell the 1952 Nobel Prize in Physics.

The modern day NMR spectrometer can now detect complex splitting patterns in 1H NMR spectra as you can see by comparing the two images.

Both show the integrated proton ratio of 1 : 2 : 3 for the HO-CH2-CH3 molecule

Note: The latter spectrum was obtained from a another source (than my usual) and shows the OH proton shift at ~4.7, similar to the 1951 result.  My original data gave the OH proton shift as 2.61 ppm.
(h) Key points and practise questions based on the 1H NMR spectrum of ethanol

Ethanol’s ¹H NMR spectrum shows three distinct signals: a triplet (~1.2 ppm, CH3), a quartet (~3.6 ppm, CH2), and a singlet (~2.5–5.0 ppm, OH), with an integration ratio of 3:2:1.

These features are diagnostic for primary alcohols.

Practice multiple choice questions based on 1H NMR spectrum of ethanol

Key ¹H NMR Signals of Ethanol

Chemical Shift (ppm) Proton Type Environment Splitting Integration
~1.2,  1.26 ppm CH3 Methyl (CH3–CH2–OH) Triplet 3H
~3.6,  2.61/4.7 ppm CH2 Methylene (CH3–CH2–OH) Quartet 2H
~2.5–5.0,  3.69 ppm OH Hydroxyl proton OH Singlet 1H

Sources: Doc Brown’s NMR notes, ChemicalBook spectrum data, Quantum-resonance.org simulation

Common Misconceptions

  • Assuming OH always appears at ~1 ppm: OH chemical shift varies widely due to hydrogen bonding and solvent effects.
  • Expecting OH splitting: OH often appears as a singlet due to rapid exchange with solvent.
  • Misidentifying triplet/quartet pattern: CH3 and CH2 splitting is mutual (n+1 rule).
  • Confusing ethanol with methanol or propan-1-ol: Integration and splitting patterns differ.
  • Confusing ethanol with methoxymethane: Methoxymethane only shows one 1H signal, both methyl groups are equivalent, not so in ethanol, CH2 not equivalent to CH3.
    •

Exam Revision Tips

  • Use integration ratios: Ethanol shows 3:2:1 for CH3:CH2:OH.
  • Apply n+1 rule: CH3 acting on CH2 → quartet; CH2 acting on CH3 → triplet.
  • Check solvent and temperature: OH peak position and splitting can vary.
  • Compare with isomers: Methoxymethane lacks OH and shows different splitting.
  • Annotate spectra: Label each peak with shift, splitting, and integration.

Practice Multiple Choice Questions based on the 1H NMR spectrum of ethanol

Each question includes feedback and distractor analysis.

Jot your responses down and check out your answers

ANSWERS to the Practice Multiple Choice Questions

Q1. What is the integration ratio of ethanol’s ¹H NMR signals?

  1. 2:2:2
  2. 3:2:1
  3. 3:2:2
  4. 5:1

Q2. What splitting pattern is observed for the CH3 group in ethanol?

  1. Singlet
  2. Doublet
  3. Triplet
  4. Quartet

Answer: C

Q3. Which signal corresponds to the CH2 group in ethanol?

  1. Singlet at ~1.2 ppm
  2. Quartet at ~3.6 ppm
  3. Triplet at ~3.6 ppm
  4. Doublet at ~2.5 ppm

Q4. Why does the OH proton often appear as a singlet?

  1. It’s not adjacent to any protons
  2. It’s shielded by CH3
  3. It undergoes rapid exchange
  4. It’s split by CH2

Q5. What causes the quartet in ethanol’s 1H NMR spectrum?

  1. CH3 coupling with OH
  2. CH2 coupling with CH3
  3. CH2 coupling with CH2
  4. OH coupling with CH2

Q6. Which molecule shows a similar NMR pattern to ethanol?

  1. Methanol
  2. Propan-1-ol
  3. Methoxymethane
  4. Ethanoic acid

Q7. What does the triplet at ~1.2 ppm indicate?

  1. CH3 group
  2. CH2 group
  3. OH group
  4. Aromatic proton

Q8. Which signal is most affected by solvent and temperature?

  1. CH3
  2. CH2
  3. OH
  4. CH3CH2

ANSWERS to the Practice Multiple Choice Questions

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

(i) Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 2 isomers of C2H6O

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 ethanol (ethyl alcohol) and methoxymethane (dimethyl ether) image sizes.

INFRARED SPECTRA: Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, the most striking difference is the broad O-H stretching band ~3400 cm-1, found in the infrared spectrum of alcohols, but absent in the infrared spectrum of ethers.

MASS SPECTRA: Both ethanol and methoxymethane show some similarities in their mass spectra, but their base ion peaks are quite different - for ethanol it is m/z 31 and for methoxymethane it is m/z 45.

1H NMR SPECTRA: The 1H NMR spectra of ethanol and methoxymethane are quite significantly different. Ethanol gives 3 peaks in the proton ratio 3:2:1 (3 different chemical environments), whereas methoxymethane only gives one 1H chemical shift peak (all 6 protons in the same chemical environment). Ethanol does not have the symmetry of methoxymethane and has the hydroxyl group, thus producing 3 different chemical environments

13C NMR SPECTRA: The 13C NMR spectra of ethanol and methoxymethane are different. Ethanol gives two 13C resonances, but methoxymethane only one (2 different 13C chemical environments and a 13C single chemical environment).

Key words & phrases: Interpreting the proton H-1 NMR spectra of ethanol, low resolution & high resolution proton nmr spectra of ethanol, H-1 nmr spectrum of ethanol, understanding the hydrogen-1 nmr spectrum of ethanol, explaining the line splitting patterns in the high resolution H-1 nmr spectra of ethanol, revising the H-1 nmr spectrum of ethanol, proton nmr of ethanol, ppm chemical shifts of the H-1 nmr spectrum of ethanol, explaining and analyzing spin line splitting in the H-1 nmr spectrum, how to construct the diagram of the H-1 nmr spectrum of ethanol, how to work out the number of chemically different protons in the structure of the ethanol organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of ethanol Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of ethanol. The proton ratio in the 1H NMR spectrum of ethanol. Deducing the number of different chemical environments of the protons in the ethanol molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of ethanol. Analysing the very high resolution 1H NMR spectrum of ultra-pure ethanol. Analysing the low resolution 1H NMR spectrum of ethanol. You may need to know the relative molecular mass of ethanol to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of ethanol. Revision notes on the proton NMR spectrum of ethanol. Matching and deducing the structure of the ethanol molecule from its hydrogen-1 NMR spectrum explaining the chemical shift splitting pattern in the 1H proton nmr of ethanol and complications in the spectra due to hydrogen bonding Explanatory diagram of the 1H H-1 proton NMR spectrum of the ethanol molecule. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of ethanol. How to explain the H-1 NMR spectrum of ethanol. The values of the integrated proton ratios in the 1-H NMR spectrum of the ethanol molecule. How to work out the molecular structure of the ethanol molecule from its proton NMR spectrum What does the H-1 proton NMR spectrum tell us about the structure and properties of the ethanol molecule? How do you interpret the H-1 NMR spectrum of ethanol C2H5OH How to interpret the H-1 NMR spectrum of ethanol C2H5OH Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the ethanol C2H5OH molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of ethanol C2H5OH. How to explain the H-1 NMR spectrum of ethanol C2H5OH. The chemical shifts and  integrated values of the proton ratios in the 1-H NMR spectrum of the ethanol C2H5OH molecule. How to work out the molecular structure of the ethanol C2H5OH molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the ethanol C2H5OH molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the ethanol C2H5OH molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of ethanol C2H5OH. interpretation diagram explaining the proton splitting pattern produced from the n+1 rule and the theoretical ratio of chemical shift and values of intensities for the proton NMR spectrum lines of ethanol C2H5OH

(j) ANSWERS to the multiple choice questions based on the 1H NMR spectrum of ethanol

Each question answer includes feedback and distractor analysis.

Q1. What is the integration ratio of ethanol’s ¹H NMR signals?

  1. 2:2:2
  2. 3:2:1
  3. 3:2:2
  4. 5:1

Answer: B

Feedback: Ethanol has 3H (CH3), 2H (CH2), and 1H (OH).

Distractors:

  • A, C & D wrong ratios

Q2. What splitting pattern is observed for the CH3 group in ethanol?

  1. Singlet
  2. Doublet
  3. Triplet
  4. Quartet

Answer: C

Feedback: CH3 is split by adjacent CH2 (2H → n+1 = 3).

Distractors:

  • A: No adjacent protons
  • B: Would require 1 adjacent proton
  • D: CH2 shows quartet

Q3. Which signal corresponds to the CH2 group in ethanol?

  1. Singlet at ~1.2 ppm
  2. Quartet at ~3.6 ppm
  3. Triplet at ~3.6 ppm
  4. Doublet at ~2.5 ppm

Answer: B

Feedback: CH2 is split by 3H of CH3 → quartet.

Distractors:

  • A: CH3 signal
  • C: Wrong splitting
  • D: OH signal varies

Q4. Why does the OH proton often appear as a singlet?

  1. It’s not adjacent to any protons
  2. It’s shielded by CH3
  3. It undergoes rapid exchange
  4. It’s split by CH2

Answer: C

Feedback: OH protons exchange rapidly, preventing coupling.

Distractors:

  • A: OH is adjacent to CH2
  • B: Not shielding-related
  • D: Splitting suppressed

Q5. What causes the quartet in ethanol’s 1H NMR spectrum?

  1. CH3 coupling with OH
  2. CH2 coupling with CH3
  3. CH2 coupling with CH2
  4. OH coupling with CH2

Answer: B

Feedback: CH2 is split by 3H of CH3 → quartet.

Distractors:

  • A/C: CH3 shows triplet
  • D: OH rarely couples

Q6. Which molecule shows a similar NMR pattern to ethanol?

  1. Methanol
  2. Propan-1-ol
  3. Methoxymethane
  4. Ethanoic acid

Answer: B

Feedback: Propan-1-ol has CH3, CH2, and OH signals.

Distractors:

  • A: No CH2–CH3 pattern
  • C: No OH
  • D: No CH3–CH2 pattern

Q7. What does the triplet at ~1.2 ppm indicate?

  1. CH3 group
  2. CH2 group
  3. OH group
  4. Aromatic proton

Answer: B

Feedback: CH2 splits another alkyl group e.g. CH3 gives triplet.

Distractors:

  • A: Quartet at ~3.6 ppm
  • C: Singlet, variable
  • D: Wrong region

Q8. Which signal is most affected by solvent and temperature?

  1. CH3
  2. CH2
  3. OH
  4. CH3CH2

Answer: C

Feedback: OH chemical shift and splitting vary with conditions.

Distractors:

  • A/B/D: Stable signals

Associated links with ethanol

H-1 proton NMR spectroscopy index

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

The infrared spectrum of Ethanol (ethyl alcohol)

The mass spectrum of Ethanol (ethyl alcohol)

The C-13 NMR spectrum Ethanol (ethyl alcohol)

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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 of ethanol - its 1H NMR spectrum is fully analysed and 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 K12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.

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