The approach for the 1nitropropane research project was to synthesize its. The most famous rearrangement is called the mclafferty rearrangement. Fred mclafferty simple english wikipedia, the free encyclopedia. In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions formed from passing. What structural requirements are necessary for a mclafferty rearrangement. Actual mass of a given isotope deviates this integer by a small but unique amount. The mass spectrum allows an experienced analyst to identify the compound or at.
Mclafferty rearrangement mass spectrometry youtube. Here, we present experimental and theoretical results of 12 model compounds that were synthesized and investigated by gctof ms and density functional theory calculations. He is best known for the mclafferty rearrangement reaction that was observed with mass. 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. Using curved arrows or hooks, show how each of these fragments can form via alpha cleavage or the mclafferty rearrangement. Which requires at least one gamma hydrogen and one site for radical cation generation. Mass spectrometry is a destructive method used to measure molecular weight and provide. Halogens, ethers, and alcohols car c eave heterolytically and homolytically 3. Nibbering laser center and chemistry department, vrije universiteit, amsterdam, the netherlands in this article, dedicated.
The mass spec of 4nonanone shows peaks at mz 58, 71, 86, 99. Mechanism of the double mclafferty rearrangement journal of. Mclafferty rearrangement is also possible in the following pathway. What is the mass of the cationic fragments from alpha cleavages. Ion source conformation is an important criterion in the level of fragmentation observed. Mass spectroscopy mass spectroscopy is a technique causing the formation of the gaseous ions with or without fragmentation. Mclafferty rearrangement simple english wikipedia, the. Most times, a carboncarbon bond breaks and the atoms do not jump across the break between the fragments. Mclafferty rearrangement of aromatics need ghydrogens. Mass spec fragmentation an extremely useful result of ei ionization in particular is a phenomenon known as fragmentation. Ppt mass spectrometry powerpoint presentation free to. Mass spectrum of 2,2,4trimethylpentane fragmentation tends to occur toward the middle of unbranched chains rather than at the ends differences in energy among allylic, benzylic, 3, 2, 1, and methyl. After ionization, a radical cation breaks apart into a cationic piece which is seen by the mass spectrometers detector plus a neutral radical piece not seen by the detector. Fragmentation of oxime and silyl oxime ether oddelectron positive ions by the mclafferty rearrangement.
Fred warren mclafferty is an american chemist known for his work in mass spectrometry. Mass spectrometry in structural and stereochemical. Mclafferty rearrangement the mclafferty rearrangement is a characteristic fragmentation of the molecular ion of a carbonyl compound containing at least one gamma hydrogen see alpha. Mass spectrometry mass spectrometer is similar to a prism. Buy interpretation of mass spectra on free shipping on qualified orders interpretation of mass spectra. A mass spectrometer bombards a substance under investigation with an electron. A mass spectrometer breaks apart the molecule being studied. 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.
Intramolecular c and 2 h isotope effects have been measured for unimolecular losses of ethene the mclafferty rearrangement from metastable molecular ions of. The structure of the product ion of a mclafferty rearrangement. The leading scientist in this field was fred mclafferty who together with frantisek turecek has written a very famous text book. The mclafferty rearrangement is a characteristic fragmentation of the molecular ion of a carbonyl compound containing at least one gamma hydrogen see alpha hydrogen.
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. Fragmentation mass spectrometry last updated december 02, 2019. Alcohols can fragment by loss of water 4 ketones can. Some of these radical cations can also rearrange after being ionized. Dec 22, 2010 mass spectrometry mass spectrometer is similar to a prism. After molecules are ionized in a mass spectrometer, they become radical cations that can then be sorted and weighed. While ketones undergo a single mclafferty rearrangement described above. Primary and secondary deuterium isotope effects are observed at the terminal and. The mclafferty rearrangement is an organic reaction seen in mass spectrometry. 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.
Chapter 2 fragmentation and interpretation of spectra 2. Request pdf fragmentation in mass spectrometry in the first part of this article, the riceramspergerkasselmarcus theory and the quasiequilibrium theory are discussed. The mclafferty rearrangement in aliphatic aldehydes and ketonesa. Mclafferty rearrangement mz 92 26 mass spectrum of noctylbenzene tropylium ion 27 naphthalene 28 unique peaks of mass spectra of some compounds 29. Fragmentation can occur in the ion source in source fragmentation where it is generally not a desired effect. 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. Molecular mass refers the average mass of molecules made. The characteristic peak occurs due to common mclafferty rearrangement. 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. This rearrangement is known as mclafferty rearrangement. Benzene c6h6 has substantial mz 79 and mz 80 peaks. One common type of rearrangement in ms is the mclafferty rearrangement which takes place in compounds that contain a carbonyl group.
Mass spectrometry dont call it spectroscopy absorption of electromagnetic radiation electron impact mass spectrometry 70 ev 1614 kcalmol contrast with energy from ir 1. Using mass number for isotopes of atoms is approximate. He is best known for the mclafferty rearrangement reaction that was observed with mass spectrometry. Is the mclafferty rearrangement of ketones concerted or. Lecture notes in eimass spectrometry by torben lund.
In the prism, light is separated into its component wavelengths which are then detected with an. The mclafferty rearrangement is a reaction observed in mass spectrometry during the fragmentation or dissociation of organic molecules. It is sometimes found that a molecule containing a ketogroup undergoes. Desired fragmentation is made in the collision zone postsource fragmentation of a tandem mass spectrometer. Instrumentation, applications, and strategies for data interpretation. The ionized molecule often fragments into smaller ionsradicals. This rearrangement, which came to be known as the mclafferty rearrangement, was first proposed for aliphatic aldehydes in 1956. The pdf version is out of date and is provided for reference purposes only. Fragmentation of oxime and silyl oxime ether oddelectron. Mass spectroscopy minnesota state university moorhead. Mass spectrometry dont call it spectroscopy absorption of electromagnetic radiation. 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. 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.
Department of organic chemistry, imm, radboud university nijmegen. Focus in honor of fred mclafferty, 2003 distinguished. Fred mclafferty simple english wikipedia, the free. The rearrangement results in the formation of charged enols and a neutral olefins. Show the results of the first ionization and show the inductive cleavage that results, with arrows. Which requires at least one gamma hydrogen and one site for.
To undergo mclafferty rearrangement, a molecule must posses a. A r adical cation is a cation with an unpaired electron. In the prism, light is separated into its component wavelengths which are then detected with an optical receptor, such as visualization. R1 c o r2 c o r1 c o r2 c o and o r1 x esters, acids, amides. Focus in honor of fred mclafferty, 2003 distinguished contribution awardee, for the discovery of the mclafferty rearrangement fred mclafferty figure 1, one of the towering figures in mass spectrometry began his career with the discovery of the rearrangement that came to be known as his reaction. Major fragmentation pattern is alhpa cleavage resulting in loss of. Mass spectrometry in structural and stereochemical problems. The radical cation that is produced when an electron is. The molecule breaks apart in consistent ways that chemists can predict. Apr 20, 2017 mclafferty rearrangement is the most important fragmentation reaction observed in the mass spectrometry. Focus in honor of fred mclafferty, 2003 distinguished contribution awardee, for the discovery of the mclafferty rearrangement fred mclafferty figure 1, one of the towering figures in mass. A new type of experiment in tandem mass spectrometry, organic mass spectrometry, 1987, 22, 6, 348wiley online library 6 j. Using curved arrows or hooks, show how each of these fragments can form via alpha cleavage or the mclafferty.
Fragmentation mass spectrometry wikimili, the free. Mass spectrum of dinbutyl ketone ix measured with an aei ms9 mass spectrometer. Feb 10, 20 this rearrangement is known as mclafferty rearrangement. 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. Mechanism of the double mclafferty rearrangement journal. The characteristic peak occurs due to common mclafferty.
The mclafferty rearrangement is an extensively studied fragmentation reaction for the oddelectron positive ions from a diverse range of functional groups and molecules. Intramolecular c and 2 h isotope effects have been measured for unimolecular losses of ethene the mclafferty rearrangement from metastable molecular ions of 2. It is an extremely great pleasure for the author to contribute an invited article to the focus section. Lowresolution mass spectrometry vs highresolution mass spectrometry highresolution mass spectrometry allows one to determine the molecular formula of a molecule 1. The hydrogen transfer reaction or the mclafferty rearrangementa. 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. Similarly, in a mass spectrometer the generated ions are separated in the mass analyzer, digitized and detected by an ion detector. The versatile role played by the mclafferty rearrangement is recognized in the mass spectra of a wide variety of organic compounds. A free powerpoint ppt presentation displayed as a flash slide show on id. The case of 1phenylpropenol, organic mass spectrometry, 1984, 19, 9, 407 wiley online library.
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