2021 Volume 36 Pages 64-77
Relative gas-phase stabilities (ΔEX) of ring-substituted 2-phenyl-1,3-dehydroadamantane-5,7-diyliums were computationally determined as the energy difference of hydride transfer equilibria between ring-substituted and its parent dications. The generating process of the dications from the corresponding neutral species were divided into two steps: the generation step of the mono-cations from the neutral species and that of the dications from the mono-cations. The ΔEX of these processes were also determined in the same manner. Obtained substituent effects were compared to those of α,α-dimethylbenzyl cations (σ+-reference) and 90˚-fixed α,α-dimethylbenzyl cations (σ0-reference). Statistical analyses revealed negligible through-resonance effects and a wide variety of saturation effects in these electron-deficient systems. The result is in contrast with those of 1-phenylcyclobutane-1,3-diyliums and 1-phenylcyclopentane-1,3-diyliums that show both significant through-resonance and saturation effects. The through-resonance and saturation effects were revealed to be independent of each other to confirm that the three-term extended Yukawa-Tsuno equation,-ΔE=ρ(σ0+r+ΔσR++S+ΔσS+), is intrinsic for substituent-effect analyses in the electron-deficient species.
