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
摘要:
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 a 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 products indicative of 3 and 4 (allyl fluoride and 1-fluoropropene) are recovered when these cations are formed in [R+ 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 C-13-labeled) allows an assessment of the primary rearrangement pathways. The distribution of label is assayed by using F-19 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.
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
作者:Thomas A. Shaler、Thomas Hellman Morton
DOI:10.1021/ja00018a009
日期:1991.8
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 a 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 products indicative of 3 and 4 (allyl fluoride and 1-fluoropropene) are recovered when these cations are formed in [R+ 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 C-13-labeled) allows an assessment of the primary rearrangement pathways. The distribution of label is assayed by using F-19 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.