フェニルアセテートアニオンに作用する直接共鳴効果の発現機構：密度汎関数法およびNBO解析による研究

抄録

Substituent effects on gas-phase stabilities of phenylacetate anions having fixed dihedral angle φ between the C-C bond in the side chain and the benzene ring plane were computationally determined at the B3LYP/6-311+G (2d,p) level of theory in addition to that of fully optimized anions. The fixed φ was varied from 0° to 90° at the interval of 10°, and the obtained 11 series of substituent effects were analyzed by the extended Yukawa-Tsuno equation (-ΔE_X=ρ(σ⁰+r^-Δσ_R+sΔσ_S)). Stabilities of parent anions showed a good correlation with sum of natural charge on the benzene ring revealing that the delocalization degree of the negative charge is the intrinsic factor governing the stabilities of the anions. The saturation degree of the anion quantified by the s value did not show a significant change against the dihedral angle φ. The through-resonance degree quantified by the r^- value increased monotonically from 0.07 to 0.53 as the increase of the φ from 0° to 90°. NBO analyses revealed that the sum of the donor-acceptor (DA) interactions from σ orbitals in the side chain to the π* orbitals in the benzene ring play an important role to induce the through-resonance effect. The detailed investigation showed that the DA interaction from the σ orbital of C-C bond to the π* orbitals in the benzene ring is the decisive factor of the tendency of the through-resonance effect.