This rearrangement is useful in structural elucidation using mass spectroscopy as the tool. The characteristic peak occurs due to common mclafferty rearrangement, with cleavage of a. The basic principle involves the fragmentation of a compound or molecule into charged species, which are accelerated, deflected, and finally focused on a detector. Mclafferty rearrangement is the most important fragmentation reaction observed in the mass spectrometry. Mass spectrum of dinbutyl ketone ix measured with an aei ms9 mass spectrometer. To undergo mclafferty rearrangement, a molecule must posses a. This rearrangement is known as mclafferty rearrangement. Some of these radical cations can also rearrange after being ionized. A molecule with mass of 44 atomic mass units, amu could be c 3h 8, c 2h 4o, co 2, or cn 2h 4. Mass spectrometry mclafferty rearrangement problems asked in previous 5 csir exams in this video we will try to understand basics of mass spectrometry. Mass spectroscopy is an analytical technique that identifies biomolecules or proteins present in biological samples and is also useful for studies on proteinprotein interactions. Most times, a carboncarbon bond breaks and the atoms do.
The book organic spectroscopy deals with uvvisible, ir, 1h nmr, c nmr, and mass spectrometry along with spectroscopic solution of the structural problems. When non mass spectrometrists are talking about mass spectrometry it rather often sounds as if they were telling a story out of poes tales of mystery and imagination. Mass spectrometry is a destructive method used to measure molecular weight and provide. Main ion an ion that corresponds to the highest intensity peak. A mclafferty type rearrangement of a trimethylsilyl group in silylated hydroxy carbonyl compounds. Ms instruments can be either low resolution lrms or high resolution hrms. Thats one half of what was originally a pair of electrons the other half is the electron which was removed in the ionisation proc. Mass spectroscopy mass spectroscopy is a technique causing the formation of the gaseous ions with or without fragmentation.
The mass spectrum of 2hexanone shows a mclafferty fragment at mz 58, while the propene fragment is not observed because it is a neutral species remember, only cationic fragments are observed in ms. Circle the fragments that are observed you may need to circle more than one answer for each. Mass spectrometry and free radicals rutgers university. Introduction, molecular ion peak and fragment ion peak of mass spectroscopy. The leading scientist in this field was fred mclafferty who together with frantisek turecek has written a very famous text book.
The mclafferty rearrangement in aliphatic aldehydes and ketonesa. Apr 20, 2017 mclafferty rearrangement is the most important fragmentation reaction observed in the mass spectrometry. Most times, a carboncarbon bond breaks and the atoms do not jump across the break between the fragments. Alcohols can fragment by loss of water 4 ketones can fragment homolytically alpha and mclafferty rearrangement. Nov 26, 2018 finally, it discusses the mclafferty rearrangement which occurs following the electron ionization of ketones. Mass spectrometry dont call it spectroscopy absorption of electromagnetic radiation. It occurs for any co including aldehydes, ketones, esters, acids, etc with a 3 or more carbon chain substituent. R1 c o r2 c o r1 c o r2 c o and o r1 x esters, acids, amides.
What is the mclafferty rearrangement in mass spectrometry. Chapter 2 fragmentation and interpretation of spectra 2. Mclafferty rearrangement major reference works wiley. It is a microanalytical technique requiring only a few nanomoles of the sample to obtain characteristic information pertaining to the structure and molecular weight of analyte. Important mass spectral rearrangements understanding mass. These reactions are well documented over the decades and fragmentation pattern is useful to. Sep 15, 2010 mechanistically, the mclafferty rearrangement can be either concerted with simultaneous hydrogen transfer and cleavage, or stepwise with the initial hydrogen transfer being followed by cleavage. This chapter book starts with a survey of the mechanisms by which organic ions can decompose and rearrange, as well as the generalized concept in terms of physicalorganic chemistry. The mass spec of 4nonanone shows peaks at mz 58, 71, 86, 99. Although these pages are not intended to be a treatise on mechanistic aspects of mass spectrometry, the mclafferty rearrangement ion is central to the identification of most ester derivatives of fatty acids, so some digression in this direction seems desirable here. Jones department of chejnistry, university of toronto, toronto, ontario received november 5, 1964 abstract the mass spectra of ethyl and isopropyl propionate and butyrate show rearrangement ions. The most famous rearrangement is called the mclafferty rearrangement.
For the analytical chemist, a mass spectrum is useful for two applications. 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. Mass spectrometry in structural and stereochemical problems. Mass spectrometry of organic ions covers the underlying theories and major applications of mass spectrometry. This is probably due to rearrangement and fragmentation is accompanied by the loss of neutral molecule. Lecture notes in eimass spectrometry by torben lund.
Mclafferty rearrangement involving the intramolecular rearrangement. Major fragmentation pattern is alhpa cleavage resulting in loss of. In the following the mclafferty formalism is used to discuss the mass spectra of aliphatic. In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions formed from passing the molecules in the ionization chamber of a mass spectrometer.
It is sometimes found that a molecule containing a ketogroup undergoes. Major fragmentation pattern is alhpa cleavage resulting in loss of sidechain and formation of acylium inon. Mclafferty rearrangement mass spectrometry youtube. Indeed, mass spectrometry appears to be regarded as a mysterious method, just good enough to supply some molecular weight information. A mass spectrometer breaks apart the molecule being studied. The fragments of a molecule cause a unique pattern in the mass spectrum. The characteristic peak occurs due to common mclafferty rearrangement. Mclafferty rearrangement simple english wikipedia, the free. After molecules are ionized in a mass spectrometer, they become radical cations that can then be sorted and weighed.
A mclaffertytype rearrangement of a trimethylsilyl group in silylated hydroxy carbonyl compounds. Rearrangement ion peak, metastable ion peak and other types peaks in mass spectroscopy mass spectroscopy is different from other forms of spectroscopy. Journal of mass spectrometry 2008, 43 12, 16731678. Halogens, ethers, and alcohols car c eave heterolytically and homolytically 3. A mass spectrum is the plot of relative abundance of ions against their mass charge ratio. Mass spectroscopy material chem 319, 422, 424 beauchamp. The molecule breaks apart in consistent ways that chemists can predict.
The versatile role played by the mclafferty rearrangement is recognized in the mass spectra of a wide variety of organic compounds. The mclafferty rearrangement is a characteristic fragmentation of the molecular ion of a carbonyl compound containing at least one gamma hydrogen see alpha hydrogen, e. The mclafferty rearrangement is an organic reaction seen in mass spectrometry. The ionized molecule often fragments into smaller ionsradicals. Mechanistically, the mclafferty rearrangement can be either concerted with simultaneous hydrogen transfer and cleavage, or stepwise with the initial hydrogen transfer being followed by cleavage. Spectroscopyspectroscopy basic theory mass spectroscopy deals with the examination of the characteristics fragments ions arising from the breakdown of organic molecules. Jan 07, 2018 the mclafferty rearrangement is the first fragmentation mechanism shown here. In h atom is transferred to the carbonyl oxygen through a 6membred transition state ts.
The mclafferty rearrangement is a reaction observed in mass spectrometry during the fragmentation or dissociation of organic molecules. Indeed, mass spectrometry appears to be regarded as a mysterious method, just good enough to. The basic aspect of organic mass spectrometry consist of bombarding. The radical cation that is produced when an electron is knocked out of a neutral closedshell molecule in eims initially possesses a lot of energy.
When nonmass spectrometrists are talking about mass spectrometry it rather often sounds as if they were telling a story out of poes tales of mystery and imagination. While ketones undergo a single mclafferty rearrangement described above, they. Mclafferty rearrangement of aromatics need ghydrogens. Observe that the h atom will be quite close to the oxygen atom in ts. Feb 10, 20 spectroscopyspectroscopy mass spectroscopy mass spectroscopy is one of the primary spectroscopic methods for molecular analysis available to organic chemist. Which requires at least one gamma hydrogen and one site for radical cation generation. Ions in mass spectrometry molecular ion an unfragmented parent ion that results from the loss of an electron by a molecule following ionization, has the same mass as the molecule sample. Using curved arrows or hooks, show how each of these fragments can form via alpha cleavage or the mclafferty rearrangement. Applications of mass spectroscopy mclafferty rearrangement of ketones these are the spectra of 3 and 4methyl2pentanone. Spectroscopyspectroscopy mass spectroscopy mass spectroscopy is one of the primary spectroscopic methods for molecular analysis available to organic chemist. The mclafferty rearrangement is the first fragmentation mechanism shown here. A radical cation is a cation with an unpaired electron. Mass spec fragmentation an extremely useful result of ei ionization in particular is a phenomenon known as fragmentation. The mclafferty rearrangement in the glu residue in a cyclic lipopeptide determined by qtof msms.
Figure 7 rearrangement of a hatom denoted rh or mclafferty rearrangement. Nov 22, 2015 this is probably due to rearrangement and fragmentation is accompanied by the loss of neutral molecule. Finally, it discusses the mclafferty rearrangement which occurs following the electron ionization of ketones. It is an extremely great pleasure for the author to contribute an invited article to the focus section. Only the combination of manual interpretation along with. This chapter book starts with a survey of the mechanisms by which organic ions can decompose and rearrange, as well as the generalized concept in. A common fragmentation pattern for larger carbonyl compounds is called the mclafferty rearrangement.
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