Site-specific hydrogen exchange and hydrogen transfer processes preceding the fragmentation of long-lived radical cations of ethyl dihydrocinnamate and related arylalkanoates

摘要: Abstract An electron ionisation study on the fragmentation of metastable molecular radical cations ethyl 3-phenylpropanoate (ethyl dihydrocinnamate) and related arylalkanoic acid esters was performed by mass-analysed ion kinetic energy (MIKE) spectrometry. Six deuterium-labelled isotopomers dihydrocinnamate were synthesised studied MIKE The leading to ions C7H7O+ (m/z 107) involving migration alkoxycarbonyl group also observed in 70-eV mass spectra alkyl dihydrocinnamates, but it found be a high-energy process that does not compete at low energies ions. Instead, undergo competing losses carbon monoxide, ethanol combined loss these neutral fragments, giving ionised styrene, C8H8•+ 104). A highly specific H/D interchange four hydrogen atoms benzylic α- ortho-positions precede [ethanol + CO]. This represents another striking case complete 4H – scrambling enables fully equilibrate interchanging prior fragmentation. mechanism rationalising observations extending previously suggested mechanisms is proposed series distonic intermediacy an ion/neutral complex. exhibit part similar behaviour, McLafferty reaction turns out more favourable with higher dihydrocinnamates. For example, n-propyl isopropyl react through distinct channels.