1131605-27-0Relevant articles and documents
Reactivity Controlling Factors for an Aromatic Carbon-Centered σ,σ,σ-Triradical: The 4,5,8-Tridehydroisoquinolinium Ion
Vinueza, Nelson R.,Jankiewicz, Bartlomiej J.,Gallardo, Vanessa A.,LaFavers, Gregory Z.,DeSutter, Dane,Nash, John J.,Kentt?maa, Hilkka I.
, p. 809 - 815 (2016)
The chemical properties of the 4,5,8-tridehydroisoquinolinium ion (doublet ground state) and related mono- and biradicals were examined in the gas phase in a dual-cell Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. The triradical abstracted three hydrogen atoms in a consecutive manner from tetrahydrofuran (THF) and cyclohexane molecules; this demonstrates the presence of three reactive radical sites in this molecule. The high (calculated) electron affinity (EA=6.06.eV) at the radical sites makes the triradical more reactive than two related monoradicals, the 5- and 8-dehydroisoquinolinium ions (EA=4.87 and 5.06.eV, respectively), the reactivity of which is controlled predominantly by polar effects. Calculated triradical stabilization energies predict that the most reactive radical site in the triradical is not position C4, as expected based on the high EA of this radical site, but instead position C5. The latter radical site actually destabilizes the 4,8-biradical moiety, which is singlet coupled. Indeed, experimental reactivity studies show that the radical site at C5 reacts first. This explains why the triradical is not more reactive than the 4-dehydroisoquinolinium ion because the C5 site is the intrinsically least reactive of the three radical sites due to its low EA. Although both EA and spin-spin coupling play major roles in controlling the overall reactivity of the triradical, spin-spin coupling determines the relative reactivity of the three radical sites.
Effects of hydrogen bonding on the gas-phase reactivity of didehydroisoquinolinium cation isomers
Vinueza, Nelson R.,Jankiewicz, Bart?omiej J.,Gallardo, Vanessa A.,Nash, John J.,Kentt?maa, Hilkka I.
, p. 21567 - 21572 (2018)
Two previously unreported isomeric biradicals with a 1,4-radical topology, the 1,5-didehydroisoquinolinium cation and the 4,8-didehydroisoquinolinium cation, and an additional, previously reported isomer, the 4,5-didehydroisoquinolinium cation, were studied to examine the importance of the exact location of the radical sites on their reactivities in the gas phase. The experimental results suggest that hydrogen bonding in the transition state enhances the reactivity of the 1,5-didehydroisoquinolinium cation towards tetrahydrofuran but not towards allyl iodide, dimethyl disulfide or tert-butyl isocyanide. The observation of no such enhancement of reactivity towards tetrahydrofuran for the 4,8-didehydroisoquinolinium and 4,5-didehydroisoquinolinium cations supports this hypothesis as these two biradicals are not able to engage in hydrogen bonding in their transition states for hydrogen atom abstraction from tetrahydrofuran. Quantum chemical transition state calculations indicate that abstraction of a hydrogen atom from tetrahydrofuran by the 1,5-didehydroisoquinolinium cation occurs at the C-1 radical site and that the transition state is stabilized by hydrogen bonding.
Experimental and computational studies on the formation of three para-benzyne analogues in the gas phase
Kirkpatrick, Lindsey M.,Vinueza, Nelson R.,Jankiewicz, Bart?omiej J.,Gallardo, Vanessa A.,Archibold, Enada F.,Nash, John J.,Kentt?maa, Hilkka I.
, p. 9022 - 9033 (2013)
Experimental and computational studies on the formation of three gaseous, positively-charged para-benzyne analogues in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer are reported. The structures of the cations were examined by isolating them and allowing them to react with various neutral reagents whose reactions with aromatic carbon-centered σ-type mono- and biradicals are well understood. Cleavage of two iodine-carbon bonds in N-deuterated 1,4-diiodoisoquinolinium cation by collision-activated dissociation (CAD) produced a long-lived cation that showed nonradical reactivity, which was unexpected for a para-benzyne. However, the reactivity closely resembles that of an isomeric enediyne, N-deuterated 2-ethynylbenzonitrilium cation. A theoretical study on possible rearrangement reactions occurring during CAD revealed that the cation formed upon the first iodine atom loss undergoes ring-opening before the second iodine atom loss to form an enediyne instead of a para-benzyne. Similar results were obtained for the 5,8-didehydroisoquinolinium cation and the 2,5-didehydropyridinium cation. The findings for the 5,8-didehydroisoquinolinium cation are in contradiction with an earlier report on this cation. The cation described in the literature was regenerated by using the literature method and demonstrated to be the isomeric 5,7-didehydro- isoquinolinium cation and not the expected 5,8-isomer. Pick the right isomer! The generation of three positively charged para-benzyne analogues was attempted in an FT-ICR mass spectrometer. The experimental and quantum chemical findings indicate that the monoradical precursors for the para-benzynes undergo ring-opening faster than formation of the para-benzyne by iodine atom elimination, thus generating enediyne isomers of the para-benzynes (see scheme). Copyright
