mass spectrum of N-methylethanamine (ethylmethylamine) C3H9N CH3NHCH2CH3 fragmentation pattern of m/z m/e ions for analysis and identification of N-methylethylamine image diagram doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Mass spectrum of N-methylethanamine

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Interpreting the mass spectrum of N-methylethanamine (ethylmethylamine)

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Mass spectroscopy - spectra index

mass spectrum of N-methylethanamine (ethylmethylamine) C3H9N CH3NHCH2CH3 fragmentation pattern of m/z m/e ions for analysis and identification of N-methylethylamine image diagram doc brown's advanced organic chemistry revision notes

N-methylethanamine, N-methylethylamine, ethylmethylamine, (c) doc b ,

Interpreting the fragmentation pattern of the mass spectrum of N-methylethanamine (ethylmethylamine)

[M]⁺ is the molecular ion peak with an m/z of 59 corresponding to [C₃H₉N]⁺, the original N-methylethanamine (ethylmethylamine) molecule minus an electron, [CH₃NHCH₂CH₃]⁺.

The small M+1 peak at m/z ?, corresponds to an ionised N-methylethanamine (ethylmethylamine) molecule with one ¹³C atom in it i.e. an ionised N-methylethanamine (ethylmethylamine) molecule of formula [¹³C¹²C₂H₉N]⁺

Carbon-13 only accounts for ~1% of all carbon atoms (¹²C ~99%), but the more carbon atoms in the molecule, the greater the probability of observing this ¹³C M+1 peak.

N-methylethanamine (ethylmethylamine) has 3 carbon atoms, so on average, ~1 in 33 molecules will contain a ¹³C atom.

The most abundant ion of the molecule under mass spectrometry investigation (N-methylethanamine (ethylmethylamine)) is usually given an arbitrary abundance value of 100, called the base ion peak, and all other abundances ('intensities') are measured against it.

Identifying the species giving the most prominent peaks (apart from M) in the fragmentation pattern of N-methylethanamine (ethylmethylamine).

Unless otherwise indicated, assume the carbon atoms in N-methylethanamine (ethylmethylamine) are the ¹²C isotope.

Some of the possible positive ions, [molecular fragment]⁺, formed in the mass spectrometry of N-methylethanamine (ethylmethylamine).

m/z value of [fragment]⁺	58	57	56	44	43	42	30	29	29	27	27
[molecular fragment]⁺	[C₃H₈N]⁺	[C₃H₇N]⁺	[C₃H₆N]⁺	[C₂H₆N]⁺	[C₂H₅N]⁺	[C₂H₅N]⁺	[CH₄N]⁺	[C₂H₅]⁺	[CH₃N]⁺	[C₂H₃]⁺	[CHN]⁺

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of N-methylethanamine (ethylmethylamine)

Atomic masses: H = 1; C = 12; N = 14

Bond enthalpies kJ/mol: C-C = 348; C-H = 412; C-N = 305; N-H = 391

Possible equations to explain the most abundant ion peaks of N-methylethanamine (ethylmethylamine) (tabulated above)

Formation of m/z 58 ion:

[CH₃NHCH₂CH₃]⁺ ===> [C₃H₈N]⁺ + H

C-H or N-H bond scission, loss of hydrogen atom from the parent molecular ion, mass change 59 - 1 = 58.

Further hydrogen atom loss will give the m/z 57 and 56 ions.

Formation of m/z 44 ion:

[CH₃NHCH₂CH₃]⁺ ===> [C₂H₆N]⁺ + CH₃

C-N or C-C bond scission, methyl group lost from parent molecular ion, mass change 59 - 15 = 44.

This is a characteristic ion formed in the mass spectrum of aliphatic amines.

The m/z 44 ion is the base peak ion, the most abundant and 'stable' ion fragment.

The m/z 44 ion can further lose hydrogen atoms to give m/z ions 43, 42, 41 and 40.

Formation of m/z 30 ion:

[CH₃NHCH₂CH₃]⁺ ===> [CH₄N]⁺ + CH₂CH₃

C-N bond scission, loss of ethyl group from the parent molecular ion, mass change 59 - 29 = 30

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