1184-60-7Relevant articles and documents
Vicinal Elimination from 2-Fluoroisopropyl Cation in the Gas Phase
Stams, Dion A.,Johri, Kamalesh K.,Morton, Thomas Hellman
, p. 699 - 706 (1988)
An electron bombardment flow (EBFlow) reactor has been used to assay C3H5+ isomer distribution from different sources.Quenching the ions by fluoride abstraction followed by 19F NMR of recovered neutral C3H5F permits analysis of the ratio of CH3C=CH2+ to allyl cation.Electron impact on 1-bromopropene yields predominantly allyl cation, in agreement with a previously reported mass spectrometric measurement.Ionization of isobutene yields an 80:20 mixture of CH3C=CH2+ and allyl cation.Electron impact on tert-butyl fluoride yields only CH3C=CH2+.The difference between the two latter results means that ionized isobutene is not an intermediate in production of C3H5+ from tert-butyl fluoride.Therefore, the major fragment of tert-butyl fluoride, (CH3)2CF+ (1), must be undergoing vicinal elimination of hydrogen fluoride to yield C3H5+.Theoretical calculations provide evidence that this does not take place via an isolated, electronically excited state of 1.Ab initio calculations on the ground-state C3H6F+ potential energy surface reveal six stable isomers of 1,3-8, all of which have stable, isoelectronic C3H6O analogues.Two of these, 7 and 8 (isoelectronic to allyl alcohol and acetone enol, respectively), correspond to ion-molecule complexes of C3H5+ and hydrogen fluoride.More extensive calculations on 8 illustrate the difference between an ion-molecule complex and a hydrogen-bonded complex.Other isomers of 1, CH3CHFCH2+ (2) and CH3CH+CH2F (11), do not have stable, isoelectonic C3H6O analogues.Neither are they stable C3H6F+ isomers.Ab initio calculations show that 2 undergoes barrier-free rearrangement to CH3CH2CHF+ (3), while 11 represents one of the resonance structures of 2-methylfluoriranium, 4.Ab initio results show good agreement with empirical estimates for ΔHf(stand.) of 3, of methylvinylfuoronium (5), and of methyl-2-propenylfluoronium (9).These lead to a calculated heat of formation of 8 that is 19 kcal/mol higher than that of 1.Ion 1 corresponds to the global energy minimum, and its two lowest energy isomers are calculated to be 3 and fluoretanium (6).Together the experimental and theoretical results show that 1 undergoes a 1,3-hydrogen shift to 8 enroute to elimination in preference to rearrangement to 6.
Reduction of fluorinated cyclopropene by nitrogenase
Ni, Feng,Lee, Chi Chung,Hwang, Candy S.,Hu, Yilin,Ribbe, Markus W.,Mckenna, Charles E.
, p. 10346 - 10352 (2013/08/23)
Reduction of the first known halogen-containing substrate by nitrogenase (N2ase), 3,3-difluorocyclopropene (DFCP), was investigated. Reduction requires both N2ase proteins (MoFe and Fe protein), ATP, and an exogenous reductant (dithionite, DT), as with N2 and known alternative substrates of the enzyme. Two major products providing evidence for reductive C-F bond cleavage were confirmed, propene (P1, requiring 6e -/6H+) and 2-fluoropropene (P2, 4e-/4H +). Both were identified by GC-MS and NMR spectroscopy, and had the same Km constants (0.022 atm, 5.4 mM). Reduction of 1,2-dideuterated DFCP (d2-DFCP) further revealed that (i) in both P1 and P2, two deuterium atoms are retained, one on carbon-1 and one on carbon-3, indicating that C=C bond cleavage rather than C-C bond cleavage is involved during DFCP reduction at least to P2 (assuming no F migration); (ii) no selectivity was observed in formation of cis and trans isomers of 1,3-d2-2- fluoropropene, whereas cis-1,3-d2-propene is the predominant 1,3-d2-propene product, indicating that one of the bound reduction intermediates on the pathway to propene is constrained geometrically. A reduction mechanism, consistent with hydride transfer as a key step, is discussed. Reductive C-F bond cleavage is an ability of N2ase that further demonstrates the unique and remarkable scope of its catalytic prowess.
Isotopomer Distributions of Neutral Products from a Doubly Labeled Cation in the Gas Phase. Interconversion of 1-Fluoro-1-propyl Cation and 1-Fluoroisopropyl Cation on the C3H6F+ Potential Energy Surface
Shaler, Thomas A.,Morton, Thomas Hellman
, p. 6771 - 6779 (2007/10/02)
The title cations CH3CH2CHF+ (3) and CH3CHCH2F+ (4) are formed as transient intermediates in the gas phase.These are labile on the millisecond timescale as free ions but can be intercepted in ion-neutral complexes.When 3 is generated as free cation by reaction of CF3+ with propionaldehyde, it rearranges to (CH3)2CF+ (1), as shown by recovery of 2-fluoropropene as a neutral product from its deprotonation in an EBFlow experiment.The same neutral product is recovered when 1 is produced directly by reaction of acetone with CF3+ in the EBFlow.Neutral productsindicative of 3 and 4 (allyl fluoride and 1-fluoropropene) are recovered when these cations are formed in + PhO.> ion-neutral complexes by electron bombardment of CH3CDFCH2OPh (6).Analysis of the isotopic distribution in the recovered neutrals from EBFlow radiolysis of CH3CDF*CH2OPh (where the asterisked carbon is 13C-labeled) allows an assessment of the primary rearrangement pathways.The distribution of label is assayed by using 19F NMR.Rearrangement of the R+ moiety to form deuterated 1 occurs in about half of the complexes formed.In the remainder, methyl transfer (to form deuterated 3) is 2-3 times faster than fluoride transfer (to form deuterated 4).Scrambling of deuterium in the neutral products provides evidence that 3 and 4 interconvert within the ion-neutral complexes.
