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McLafferty Rearrangement (mclafferty + rearrangement)
Selected AbstractsMcLafferty rearrangement of the radical cations of butanal and 3-fluorobutanal: A theoretical investigation of the concerted and stepwise mechanismsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2008Daniel Norberg Abstract The stepwise and concerted pathways for the McLafferty rearrangement of the radical cations of butanal (Bu+) and 3-fluorobutanal (3F-Bu+) are investigated with density functional theory (DFT) and ab initio methods in conjunction with the 6-311+G(d,p) basis set. A concerted transition structure (TS) for Bu+, (H), is located with a Gibbs barrier height of 37.7 kcal/mol as computed with CCSD(T)//BHandHLYP. Three pathways for the stepwise rearrangement of Bu+ have been located, which are all found to involve different complexes. The barrier height for the H, transfer is found to be 2.2 kcal/mol, while the two most favorable TSs for the C,,C, cleavage are located 8.9 and 9.2 kcal/mol higher. The energies of the 3F-Bu+ system have been calculated with the promising hybrid meta-GGA MPWKCIS1K functional of DFT. Interestingly, the fluorine substitution yields a barrier height of only 20.5 kcal/mol for the concerted TS, (3F-H). A smaller computed dipole moment, 12.1 D, for (3F-H) compared with 103.2 D for (H) might explain the stabilization of the substituted TS. The H, transfer, with a barrier height of 4.9 kcal/mol, is found to be rate-determining for the stepwise McLafferty rearrangement of 3F-Bu+, in contrast to the unsubstituted case. By inspection of the spin and charge distributions of the stationary points, it is noted that the bond cleavages in the concerted rearrangements are mainly of heterolytic nature, while those in the stepwise channels are found to be homolytic. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Characterization of different poly(2-ethyl-2-oxazoline)s via matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2009Anja Baumgaertel Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) coupled with CID (collision-induced dissociation) has been used for the detailed characterization of two poly(2-ethyl-2-oxazoline)s as part of a continuing study of synthetic polymers by MALDI-TOF MS/MS. These experiments provided information about the variety of fragmentation pathways for poly(oxazoline)s. It was possible to show that, in addition to the eliminations of small molecules, like ethene and hydrogen, the McLafferty rearrangement is also a possible fragmentation route. A library of fragmentation pathways for synthetic polymers was also constructed and such a library should enable the fast and automated data analysis of polymers in the future. Copyright © 2009 John Wiley & Sons, Ltd. [source] Fragmentation Mechanism of Trans -,-Aryl-,-enamino EstersCHINESE JOURNAL OF CHEMISTRY, Issue 8 2002Nan Jiang Abstract Electron impact-induced fragmentation mechanisms of trans-, -aryl- , -enamino esters were investigated using mass-analyzed ion kinetic energy (MIKE) spectrometry and high resolution accurate mass data. It was found that the main characteristic fragmentations of compounds studied were: an odd electron ion M+ - EtOH was formed by losing a neutral molecule of ethanol; and the skeletal rearrangements took place; and the ring opening reaction happened after losing a carbon monoxide; and the typical McLafferty rearrangement underwent in ester group. The cyclization reaction caused by losing neutral molecule of TsNH2 due to the ortho -effects of substituted group of aromatic ring was also observed. [source] | ||||||||||