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