94498-96-1Relevant academic research and scientific papers
The stepwise nature of the γ-hydrogen rearrangement in unsaturated ions
Ture?ek, Franti?ek,Drinkwater, Donald E.,McLafferty, Fred W.
, p. 993 - 997 (2007/10/02)
The mechanism of acetaldehyde elimination from the benzyl ethyl ether cation radical (1) yielding C7H8?+ ions is re-examined. A distonic ion intermediate (2) pertinent to a stepwise route is generated independently by dissociative ionization of 3-methyl-2,4-dioxaspiro[5.5]undeca-8,10-diene and by reaction of the methylenecyclohexa-2,4-diene cation radical with acetaldehyde. Metastable 1 and 2 differ in the kinetic energy released upon dissociation (Tav=7.0 and 1.1 kJ mol-1, respectively), indicating an energy barrier to the isomerization 1 → 2. During low-energy dissociation of 2 another C7H8?+ isomer, probably the more stable toluene cation radical, is also formed. This apparently takes place in an ion-molecule complex with acetaldehyde via reversible hydrogen transfer involving the acetaldehyde oxygen atom and represents an entropy bottleneck of the elimination. These competing second steps should produce D/H and the 18O/16O isotope effects in addition to the D/H effect of the first step 1 → 2, accounting for the observations by Bowie, Derrick, et al. attributed to a concerted mechanism; we believe this to be the first case involving this mechanism for a double isotope effect in a stepwise reaction. The kinetic energy release data, intermediate preparation and dissociation, and product characterization by collisionally activated dissociation spectra support a stepwise mechanism.
Gas-Phase Wittig Rearrangement of Carbanions Derived from Benzyl Ethers
Eichinger, Peter C. H.,Bowie, John H.,Blumenthal Thomas
, p. 5078 - 5082 (2007/10/02)
The CA mass spectra of ions PhC-HOR and Ph(R)CH-O- (R = alkyl and phenyl) are very similar, suggesting that the Wittig rearrangement PhC-HOEt -> Ph(Et)CH-O- occurs in the gas phase.Major fragmentation can be interpreted in terms of 1,2-elimination of groups from the Wittig product ion.For example, 2H labeling of PhC-HOEt and Ph(Et)CH-O- show that the major processes produce Me-CH=CH-O- + C6H6 and (C6H4)-CHO + C2H6, with the latter process involving prior scrambling of phenyl hydrogens.An analogous process, Ph2CH-O- -> (C6H4)-CHO + C6H6 gives the major peak in the spectrum of "PhC-HOPh".
