mass spectrum of ethyl ethanoate fragmentation pattern of m/z m/e ions for analysis and identification of ethyl acetate image diagram doc brown's advanced organic chemistry revision notes

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Advanced Organic Chemistry: Mass spectrum of ethyl ethanoate

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The mass spectrum of ethyl ethanoate (ethyl acetate)

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing mass spectra of ethyl ethanoate

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Mass spectroscopy - spectra index

mass spectrum of ethyl ethanoate fragmentation pattern of m/z m/e ions for analysis and identification of ethyl acetate image diagram doc brown's advanced organic chemistry revision notes

Interpreting the fragmentation pattern of the mass spectrum of ethyl ethanoate

Ethyl ethanoate C₄H₈O₂ , , ,

[M]⁺ is the molecular ion peak (M) with an m/z of 88 corresponding to [C₄H₈O₂]⁺, the original ethyl ethanoate molecule minus an electron, [CH₃COOCH₂CH₃]⁺.

You might see a tiny M+1 peak at m/z 89, corresponding to an ionised ethyl ethanoate molecule with one ¹³C atom in it i.e. an ionised ethyl ethanoate molecule of formula ¹³C¹²C₃H₈O₂

Identifying the species giving the most prominent peaks (apart from M) in the fragmentation pattern of ethyl ethanoate.

m/z value of [fragment]⁺	73	70	61 ?	45	43	42	29	27	15
[molecular fragment]⁺	[C₂H₅O-C=O]⁺	[C₄H₆O]⁺	[C₂H₄O₂]⁺	[C₂H₅O]⁺	[CH₃C=O]⁺	[CH₂CO]⁺	[CH₃CH₂]⁺	[C₂H₃]⁺	[CH₃]⁺

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of ethyl ethanoate

Atomic masses: H = 1; C = 12 (13 for ~1 in 100); O = 16

Bond enthalpies = kJ/mol: C-C = 348; C-H = 412; C-O = 360; C=O = 743

Explaining the principal fragments of the mass spectrum of ethyl ethanoate

The most abundant ion peaks

Formation of m/z 73 ion:

[CH₃COOCH₂CH₃]⁺ ===> [C₂H₅O-C=O]⁺ + CH₃

C-C bond scission in the parent molecular ion, mass change 88 - 15 = 73.

Formation of m/z 70 ion:

[CH₃COOCH₂CH₃]⁺ ===> [C₄H₆O]⁺ + H₂O

Elimination of water from the parent molecular ion?, mass change 88 - 18 = 70

Formation of m/z 45 ion:

[CH₃COOCH₂CH₃]⁺ ===> [C₂H₅O]⁺ + CH₃CO

C-C bond scission in the parent molecular ion, mass change 88 - 43 = 45.

Formation of m/z 43 ion:

[CH₃COOCH₂CH₃]⁺ ===> [CH₃C=O]⁺ + CH₃

C-C bond scission in the parent molecular ion, mass change 88 - 45 = 43.

The m/z 43 ion is the base peak ion, the most abundant 'stable' ion fragment.

Formation of m/z 15 ion:

[CH₃COOCH₂CH₃]⁺ ===> [CH₃]⁺ + C₃H₅O₂

C-C bond scission in the parent molecular ion, mass change 88 - 73 = 15

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Links associated with ethyl ethanoate

The infrared spectrum of Ethyl ethanoate (ethyl acetate)

The H-1 NMR spectrum of Ethyl ethanoate (ethyl acetate)

The C-13 NMR spectrum of Ethyl ethanoate (ethyl acetate)

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