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Question
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4. Identify all of the fatty acid methyl esters Using the gas chromatography data, place a check next to the predominant fatty acid (represented by its fatty acid in your mixture by their corresponding M" peak in the mass spectrum. methyl ester) present in your oil or fat? Using reputable internet resources or your textbook, what human health characteristics have been linked to that fatty acid? FAME name) s. Go through your mass spectra and eircle all evidence of M-31 peaks. Explain why your fatty esters may contain an M-31 peak. vour mas spectra and cirede all erid f M-Jl peak Expawhyyour faty acid methy1
Explanation / Answer
1.
The molecular ion at m/z = 270 is clearly seen that mass of the compound is 270. It is an ion at 239 ([M-31]+) representing loss of a methoxyl group, and confirming that it is indeed a methyl ester.
An ion at m/z = 227 ([M-43]+) and ion at m/z = 74 represent loss of a C3 unit (carbons 2 to 4) along with via a complex rearrangement, McLafferty rearrangement ion.
The separation of most of the peaks by 14 and 28 mass units and appearance of CnH2n+1 and CnH2n-1 ion series also confirmed its long chain aliphatic nature
On the basic of the above the compound is methyl palmitate.
2.
The molecular ion at m/z = 294 is clearly seen that mass of the compound is 294
It is an ion at 263 ([M-31]+) representing loss of a methoxyl group.
An ion at m/z = 220 and ion at m/z = 74 represent a McLafferty rearrangement ion.
The separation of most of the peaks by 14 and 28 mass units and appearance of CnH2n+1 and CnH2n-1 ion series also confirmed its long chain aliphatic nature
On the basic of the above the compound is methyl linoleate.
3.
The molecular ion at m/z = 296 is clearly seen that mass of the compound is 296
It is an ion at 264 ([M-32]+) representing loss of a methoxyl group along with Hydrogen atom
An ion at m/z = 222 and ion at m/z = 74 represent a McLafferty rearrangement ion.
The separation of most of the peaks by 14 and 28 mass units and appearance of CnH2n+1 and CnH2n-1 ion series also confirmed its long chain aliphatic nature
On the basic of the above the compound is methyl oleate.
Reference is http://lipidlibrary.aocs.org/ms/ms03b/file.pdf,
A.V. Bailey, et al, J. Am.OIL Chem.Soc.,48, 775 (1971).
G.S. Whitby, et al, J.Chem.Soc., 1458 (1926).
Viscardo Malta, Giancarlo Celotti, Roberto Zannetti and Adele Ferrero Martelli, “Crystal structure of the C from of stearic acid” J. Chem. Soc., B, 548, (1971).
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