2,5—二取代苯醌键长异常的EHMO研究

D■hne等曾指出,一些2,5—二取代对苯醌Ⅰ可视为两个取代三甲川共轭链Ⅱ的偶合物,如Ⅲ所示.在这一假设基础上,Ⅰ的一些物理、化学性质能得到满意解释.近年来晶体结构测定结果表明,在分子Ⅰ(X=NRR’,O~-)中,C_1-C_2(或C_4-C_5)键长为1.51-1.55(?),反常地长于标准的C_(sp~2)-C_(sp~2)键长值,而C_2-C_3和C_3-C_4键长却明显地均匀化.D(?)hne等最近认为这是偶合假设的又一证明:所讨论的键长均匀化正是     

取代芳杂环及其苯并物的共振能和互变异构

取代芳杂环及其苯并物在溶液中的互变异构平衡实验结果已有大量报道。互变异构体的芳性或共振能(RE)被广泛用于定性解释互变平衡的移动趋向,Katritzky 等并从互变平衡实验数据得出吡啶酮、喹诺酮和异喹诺     

定量共振论与MO的关系——奇共轭烃的激发态

Quantified resonance theory (QRT) involving the use of weighting has been applied to ionization potential, electron affinity, energy of the lowest π→π~* transiton, charge density and bond order in excited state for odd π hydrocarbon radicals, anions and cations, the QRT results are in remarkable agreement with HMO, the heteroatom effects on these properties obtained by QRT are in full accord with PMO. Moreover QRT gives a simple rule for estimating whether odd nonalternant hydrocarbons containing a 5-or 7-membered ring have NBMO or not.