A mass spectrometer breaks apart the molecule being studied. The base peaks of phthalate esters with alkyl side chains except dimethyl phthalate were mz 149, indicating that their fragmentation pathways were similar. In this article, dedicated to professor fred mclafferty, i wish to recollect early observations with regard to the rearrangement named after him for 1nitropropane and the methyl ester of. Mass spectroscopy minnesota state university moorhead. Actual mass of a given isotope deviates this integer by a small but unique amount. I would recommend looking at introduction to mass spectrometry by j. Journal of mass spectrometry 2008, 43 12, 16731678. A frame time of the main theoretical milestones in both theory and experimental mass spectrometry is highlighted here. Mclafferty rearrangement of aromatics need ghydrogens. Mclaffertytype rearrangements preceding fragmentation were found as their main fragmentation pathway. Mass spectra of new functionally substituted heterocycles. Using mass number for isotopes of atoms is approximate. For the analytical chemist, a mass spectrum is useful for two applications.
Most times, a carboncarbon bond breaks and the atoms do. Magneticsector mass spectrometry mass spectroscopy alireza ghassempour phd. Is the mclafferty rearrangement of ketones concerted or. Gas chromatographytandem mass spectrometry was applied to study the mass spectral fragmentation of phthalate esters. Mass spectral fragmentation pathways of phthalate esters. Mclafferty rearrangement simple english wikipedia, the. In the prism, light is separated into its component wavelengths which are then detected with an optical receptor, such as visualization.
Intramolecular c and 2 h isotope effects have been measured for unimolecular losses of ethene the mclafferty rearrangement from metastable molecular ions of 2. The mass spectrum of an aldehyde shows a parent peak at mz 58 and a base peak at mz 29. Mass spectrometry of some butyrophenones frigerio 1972. Mclafferty rearrangement of the radical cations of butanal and 3fluorobutanal.
First, the fundamental notions of mass spectrometry are explained, so that the reader. The mclafferty rearrangement produces oddelectron fragment ions with even. Observe that the h atom will be quite close to the oxygen atom in ts. Ppt mass spectrometry powerpoint presentation free to. Leaves and stems by liquid chromatographytandem mass spectrometry by sarina m. Fred mclafferty is a professor of chemistry at cornell university. The mass spec of 4nonanone shows peaks at mz 58, 71, 86, 99. The mclafferty rearrangement is the first fragmentation mechanism shown here.
Interpretation of mass spectra paperback january 1, 1966 by fred w. He is also known for electron capture dissociation, a method of fragmenting gas phase ions. Mclafferty rearrangement mz 92 26 mass spectrum of noctylbenzene tropylium ion 27 naphthalene 28 unique peaks of mass spectra of some compounds 29 mass spectrum of unknown compound 30. Mass spectrometry mass spectrometer is similar to a prism.
Some of these radical cations can also rearrange after being ionized. A mclafferty type rearrangement of a trimethylsilyl group in. The basic aspect of organic mass spectrometry consist of bombarding. This rearrangement occurs for both cases clearly in a stepwise fashion, although for the ester, it occurs as a hidden rearrangement that catalyzes the tautomerization of the nitro group. It is an extremely great pleasure for the author to contribute an invited article to the focus section. The mclafferty rearrangement in the glu residue in a cyclic lipopeptide determined by qtof msms. Fred mclafferty simple english wikipedia, the free. With roland gohlke, he pioneered the technique of gas chromatographymass spectrometry. Mass spectrometry cleavage, inductive cleavage and the mclafferty rearrangement produce important fragments that are observed in mass spectra of aldehydes and ketones. Chapter 2 fragmentation and interpretation of spectra 2. A radical cation is a cation with an unpaired electron. Data are given for a large number of hydroxy acids and hydroxy ketones including aldonic acids. Predict some signals that you would expect to see in a mass spectrum of 2chloropropane. He is best known for the mclafferty rearrangement reaction that was observed with mass spectrometry.
When students ask what books to read on mass spectrometry, there are various excellent monographs, but the ideal textbook still seemed to be missing at least in my opinion. Istituto di ricerche farmacologiche mario negri, via eritrea 62, 20157 milano, italy. The pdf version is out of date and is provided for reference purposes only. Mechanism of the double mclafferty rearrangement journal. The hydrogen transfer reaction or the mclafferty rearrangementa. Coordination of sodium cation to the oxygen functions may either lead to formation of a fivemembered or a sixmembered ring. After molecules are ionized in a mass spectrometer, they become radical cations that can then be sorted and weighed. Mass spectrometry lecture 4 interpreting electron impact mass spectra continued recommended.
View enhanced pdf access article on wiley online library html view download pdf for offline viewing. Figure 7 rearrangement of a hatom denoted rh or mclafferty rearrangement. Spectroscopyspectroscopy basic theory mass spectroscopy deals with the examination of the characteristics fragments ions arising from the breakdown of organic molecules. Sodium adducts of anti2,3dihydroxy1phenylpentane1,4dione compounds with different substituents were studied by collisioninduced dissociation.
The approach for the 1nitropropane research project was to synthesize its. The mass spectrum allows an experienced analyst to identify the compound or at. Primary and secondary deuterium isotope effects are observed at the terminal and positions, respectively. Comprehensive study of the phenolics and saponins from helleborus niger l. Mclafferty author see all 7 formats and editions hide other formats and editions. Marcuskassel rrkm theory to fit the conditions of mass spectrometry and it. The larger ring ketones give surprisingly intense mclafferty plus one ions at mz 59, which is the base peak in the mass spectrum of cyclohexylacetone.
The mclafferty rearrangement is a reaction observed in mass spectrometry. Mass spectrometry lecture 4 interpreting electron impact mass spectra ch 908. The base peaks of benzyl butyl phthalate and dibutoxyethyl phthalate were also at mz 149. A mass spectrum is the plot of relative abundance of ions against their masscharge ratio. The characteristic peak occurs due to common mclafferty rearrangement, with cleavage of a.
Nibbering laser center and chemistry department, vrije universiteit, amsterdam, the netherlands in this article, dedicated to professor fred mclafferty, i wish to recollect early observations with regard to the rearrangement named after him for 1nitropropane and the methyl ester of. The most famous rearrangement is called the mclafferty rearrangement. Mass spectrometry in structural and stereochemical. Fred warren mclafferty is an american chemist known for his work in mass spectrometry. The mclafferty rearrangement is an organic reaction seen in mass spectrometry.
On the mclafferty and double hydrogen rearrangements in. In the second part of the chapter, the molecular fragmentation for alkanes, isoalkanes. Abundant rearrangement ions are formed for me 3si derivatives of. In the electron impact mass spectra of a series of cycloalkylacetones with ring sizes varying from cyclopropane to cycloheptane, the intensity of the mclafferty rearrangement ion at mz 58 increases with the larger, less strained rings. While ketones undergo a single mclafferty rearrangement described above. Mass spectra at 20 ev of the tms derivatives of ribonic acid i, ribaric acid 11 and ribulose ill. It is sometimes found that a molecule containing a ketogroup undergoes.
Mass spectrum of dinbutyl ketone ix measured with an aei ms9 mass spectrometer. Interpretation of mass spectra, say the authors, aims at correlating ion dissociation mechanisms on a much broader scale, with emphasis on basic attributes such as ionization energies, proton affinities, and bond dissociation energies. Fragmentation of oxime and silyl oxime ether oddelectron positive ions by the mclafferty rearrangement. Lithiated 11ethoxyethoxyallene and methoxymethyl isothiocyanate. They stress that the most important part of learning how to interpret unknown mass spectra is to practise doing it. Electroninduced ionization of undeuterated and deuterated. What is the mclafferty rearrangement in mass spectrometry. The mclafferty rearrangement is a characteristic fragmentation of the molecular ion of a carbonyl compound containing at least one gamma hydrogen see alpha hydrogen. The leading scientist in this field was fred mclafferty who together with frantisek turecek has written a very famous text book. A mclafferty type rearrangement of a trimethylsilyl group. Mclafferty rearrangement is the most important fragmentation reaction observed in the mass spectrometry. Using curved arrows or hooks, show how each of these fragments can form via alpha cleavage or the mclafferty rearrangement. Focus in honor of fred mclafferty, 2003 distinguished.
The molecule breaks apart in consistent ways that chemists can predict. This rearrangement may take place by a radical or ionic mechanism. A mclaffertytype rearrangement of a 3si megroup is demonstrated. Request pdf fragmentation in mass spectrometry in the first part of this article, the riceramspergerkasselmarcus theory and the quasiequilibrium theory are discussed. Similarly, in a mass spectrometer the generated ions are separated in the mass analyzer, digitized and detected by an ion detector. Competitive mclaffertytype rearrangements of sodium. Major fragmentation pattern is alhpa cleavage resulting in loss of sidechain and formation of acylium inon. Mass spectrometry dont call it spectroscopy absorption of electromagnetic radiation electron impact mass spectrometry 70 ev 1614 kcalmol contrast with energy from ir 110 kcalmol or nmr 0. Mclafferty rearrangement mass spectrometry youtube.
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