13C nmr spectrum of ethyl ethanoate analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of ethyl acetate doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: ¹³C NMR spectrum of ethyl ethanoate CH₃COOCH₂CH₃

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Interpreting the Carbon-13 NMR spectrum of ethyl ethanoate (ethyl acetate)

[Author © Dr Phil Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses, IB chemistry & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy analysis of ethyl ethanoate [spectrum page updated RE-EDIT]

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C-13 NMR spectroscopy - spectra index

Introductory note on the 13C NMR spectrum of ethyl ethanoate

Students and teachers please note that my explanation of the carbon-13 NMR spectrum of ethyl ethanoate is designed for advanced, but pre-university, chemistry courses.

The description does not involve the chemical shift δ spin-spin coupling effects for ethyl ethanoate and the relative size of the carbon-13 NMR shifts does not give the ratio of the carbon atoms in the different non-equivalent chemical environments of the ethyl ethanoate molecule.

The most common solvent used for investigating the C13 NMR spectrum of compounds like ethyl ethanoate, is CDCl₃ and other deuterated solvents.

C-13 nmr spectrum of ethyl ethanoate analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of ethyl acetate doc brown's advanced organic chemistry revision notes

TMS is the acronym for tetramethylsilane, formula Si(CH₃)₄, whose ¹³C atoms are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in ¹³C NMR spectroscopy and all other ¹³C shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the ¹³C atoms in an organic molecule - ethyl ethanoate here.

Ethyl ethanoate C₄H₈O₂ , , ,

The molecular structure and naming of carboxylic acids and derivatives
Interpreting the C-13 NMR spectrum of ethyl ethanoate

As you can see from the diagram above there are only 4 chemical ¹³C shift lines in the C-13 NMR spectrum of ethyl ethanoate indicating 4 different chemical environments of the carbon atoms.

ethyl ethanoate , , ,

CH₃COOCH₂CH₃

(Note the 4 colours indicating the 4 different chemical environments of the carbon atoms in ethyl ethanoate, so all 4 carbon atoms in ethyl ethanoate occupy different chemical environments).

¹³C carbon atoms adjacent very electronegative elements like oxygen, tend to show larger ¹³C NMR chemical shifts.

The carbon-13 NMR spectra a provides direct evidence of 4 different carbon atom environments in the ethyl ethanoate molecule from four different chemical shifts (ppm).

The 13C NMR pattern of chemical shifts can help distinguish isomers of ethyl ethanoate

See also Isomers of molecular formula C₄H₈O₂ for other isomeric structures and brief notes on the 13C NMR chemical shifts.

Practise exam questions based on the 13C NMR spectrum of ethyl ethanoate

Five multiple choice questions with worked out answers an full explanations based on the 13C NMR spectrum of ethyl ethanoate

These questions are an experiment of doc brown using AI to generate practice exam questions based on typical specifications of UK A-level chemistry exam boards - I have checked and re-edited the questions where necessary, if you think there is any error PLEASE email me at chem55555@hotmail.com asap.

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

ANSWERS

Ethyl ethanoate (CH₃COOCH₂CH₃) Distinct carbon 13C chemical environments:

Carbonyl carbon (C=O)
Methyl carbon next to carbonyl (CH₃CO–)
Methylene carbon next to oxygen (–OCH₂–)
Terminal methyl carbon (–CH₃)

Chemical shift ranges (A‑level):

C=O (ester): ~170–175 ppm
C next to O: ~60 ppm
C next to C=O: ~20 ppm
Alkyl CH3: ~14 ppm

1. A strong peak appears around 170–175 ppm. Which carbon does this correspond to?

A. The carbonyl carbon

B. The terminal methyl carbon

C. The methylene carbon next to oxygen

D. The methyl carbon next to the carbonyl

2. A peak near 60 ppm is observed. Which carbon produces this signal?

A. The carbonyl carbon

B. The terminal methyl carbon

C. The methylene carbon next to oxygen

D. The methyl carbon next to the carbonyl

3. A peak around 20 ppm appears in the spectrum. Which carbon does this correspond to?

A. The methyl carbon next to the carbonyl

B. The carbonyl carbon

C. The methylene carbon next to oxygen

D. The terminal methyl carbon

4. How many distinct carbon environments appear in the ¹³C NMR spectrum of ethyl ethanoate?

A. Three

B. Four

C. Five

D. Six

Correct answer: B — Four

5. Which combination of chemical shifts is most characteristic of an ester such as ethyl ethanoate?

A. 14 ppm and 20 ppm

B. 14 ppm and 170 ppm

C. 20 ppm and 60 ppm

D. 60 ppm and 170 ppm

ANSWERS

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The infrared spectrum of Ethyl ethanoate

The mass spectrum of Ethyl ethanoate (ethyl acetate)

The H-1 NMR spectrum of ethyl methanoate (ethyl formate)

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ANSWERS

Five multiple choice questions with worked out answers an full explanations based on the 13C NMR spectrum of ethyl ethanoate

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

Ethyl ethanoate (CH₃COOCH₂CH₃) Distinct carbon 13C chemical environments:

Carbonyl carbon (C=O)
Methyl carbon next to carbonyl (CH₃CO–)
Methylene carbon next to oxygen (–OCH₂–)
Terminal methyl carbon (–CH₃)

Chemical shift ranges (A‑level):

C=O (ester): ~170–175 ppm
C next to O: ~60 ppm
C next to C=O: ~20 ppm
Alkyl CH3: ~14 ppm

1. A strong peak appears around 170–175 ppm. Which carbon does this correspond to?

A. The carbonyl carbon

B. The terminal methyl carbon

C. The methylene carbon next to oxygen

D. The methyl carbon next to the carbonyl

Correct answer: A — The carbonyl carbon

Explanation: The C=O carbon in an ester is highly deshielded and appears far downfield, typically 170–175 ppm. This is always the most downfield peak in the spectrum.

Common misconception: Students sometimes think the carbon next to oxygen is the most downfield — but carbonyl carbons dominate the ¹³C spectrum.

2. A peak near 60 ppm is observed. Which carbon produces this signal?

A. The carbonyl carbon

B. The terminal methyl carbon

C. The methylene carbon next to oxygen

D. The methyl carbon next to the carbonyl

Correct answer: C — The methylene carbon next to oxygen

Explanation: Carbons bonded to oxygen are strongly deshielded, giving shifts around 60 ppm. This identifies the –OCH₂– group of the ethyl chain.

Common misconception: Students often confuse “next to oxygen” with “next to carbonyl”. Carbonyl deshielding is much stronger and appears far downfield (~170 ppm).

3. A peak around 20 ppm appears in the spectrum. Which carbon does this correspond to?

A. The methyl carbon next to the carbonyl

B. The carbonyl carbon

C. The methylene carbon next to oxygen

D. The terminal methyl carbon

Correct answer: A — The methyl carbon next to the carbonyl

Explanation: The CH₃CO– carbon is moderately deshielded by the carbonyl group, giving a shift around 20 ppm.

Common misconception: Students sometimes think this peak belongs to the terminal CH₃, but that appears further upfield (~14 ppm).

4. How many distinct carbon environments appear in the ¹³C NMR spectrum of ethyl ethanoate?

A. Three

B. Four

C. Five

D. Six

Correct answer: B — Four

Explanation: Ethyl ethanoate contains four chemically distinct carbons:

C=O
CH₂CO–
–OCH₂–
–CH₃ (ethyl)

Common misconception: Students sometimes assume “each carbon gives a peak”, but symmetry can reduce the number — here, the two methyl groups are not equivalent.

5. Which combination of chemical shifts is most characteristic of an ester such as ethyl ethanoate?

A. 14 ppm and 20 ppm

B. 14 ppm and 170 ppm

C. 20 ppm and 60 ppm

D. 60 ppm and 170 ppm

Correct answer: D — 60 ppm and 170 ppm

Explanation: Esters show two highly diagnostic carbon environments:

C=O at ~170 ppm
C–O at ~60 ppm

Together, these confirm the presence of an ester functional group.

Common misconception: Students often rely only on the carbonyl peak, but C–O carbons are essential for distinguishing esters from aldehydes/ketones.