Development of Structure-Reactivity Relationship

(1)利用Yukawa-Tsuno(Y-T)方程分析了取代基对苯甲醛、苯乙酮、苯甲酸甲酯、二苯甲酮和硝基苯的电子亲和能对芳香族自由基稳定性的影响。结果表明，体系的共振需求参数(R)变化很大，从硝基苯的0.62到苯甲醛的1.11，再到苯甲酸甲酯系列的1.29。R值的增加顺序与母体自由基阴离子稳定性的降低一致。(2)根据质子转移平衡，测定了在β位置含有CF3、t-Bu、Me或H基团的m，p-取代苯乙炔的气相碱性(GB)。基于Y-T方程的取代基对Gb值的影响分析表明，随着各系列未取代成员稳定性的降低，乙烯基阳离子的共振性需求增加。结果表明，r值与母体阳离子的稳定性之间有很好的线性关系，这表明共振需求是碳正离子结构中固有的参数。(3)为了证实碳正离子自由基阴离子体系的共振需求的特征，进行了从头算分子轨道计算。结果表明，碳正离子体系中键长等结构参数的变化符合共振理论，并与观察到的气相离子的共振需求呈线性相关。总之，由Y-T关联确定的经验r值应该具有真实的物理意义，它代表了正电荷的pi离域程度。

(1) Substituent effects on the stability of aromatic radical anions measured by electron affinities of benzaldehydes, acetophenones, methyl benzoates, benzophenones, and nitrobenzenes were analyzed by means of the Yukawa-Tsuno (Y-T) equation. It has been shown that resonance demand parameter (r) varies significantly with the system from 0.62 for nitrobenzene, via 1.11 for benzaldehyde, to 1.29 for methyl benzoate series. The increasing order of the r value is in agreement with decreasing stability of a parent radical anion. This trend is consistent with that observed for benzylic carbocations.(2) Gas-phase basicities (GB) of m, p-substituted phenylacetylenes having the CF_3, t-Bu, Me, or H group at the beta-position have been determined based on proton-transfer equilibria. The analysis of the substituent effects on the GB values based on the Y-T equation showed that the resonance demand of the vinyl cation increases with the decreasing stability of the unsubstituted member of respective series. It was found that there is a good linear relationship between the r values and the stabilities of the respective parent cations, including the benzylic carbocation series, suggesting that the resonance demand is a parameter inherent in the structure of a carbocation.(3) In order to corroborate the characterization of the resonance demands for the carbocation radical anion systems, ab initio MO calculations were performed. It was found that the changes of structural parameters such as a bond length in the carbocation system are in consistent with the resonance theory and that those are linearly correlated with the resonance demand observed for gas-phase ions. In conclusion, the empirical r value determined by the Y-T correlation should have real physical meaning which represents the degree of pi-delocalization of the positive charge.