立体拥挤二苯基卡宾分子结构的电子效应

通过对二苯基重氮甲烷的光照射产生了一系列具有对称对位取代基的三线态二 (2 ,6 二甲苯基 )卡宾 .用电子顺磁共振波谱对其进行了研究 .通过对不同粘度的基质 (matrix)中零磁场分裂参数D和E的测定 ,依据电子自旋离域取代基常数σ 对三线态二苯基卡宾的分子结构的取代基效应进行了分析 .并通过对卡宾的热消失温度及其室温脱气苯溶液中寿命的测定 ,对三线态二 (2 ,6 二甲苯基 )卡宾的稳定性进行了定量考察 .结果表明 ,对卡宾中心的自旋电子具有离域效应的取代基使三线态二 (2 ,6 二甲苯基 )卡宾采取低能稳定的直线型结构 ,且显示了更好的热稳定性和更长的寿命 .

Electronic Effect on the Molecular Structure of Sterically Congested Triplet Diphenylcarbenes

Carbenes are important reactive intermediates in a variety of chemical reaction, and therefore have been extensively studies both experimentally and theoretically to explore their chemical properties and various parameters that affect their stabilities. In order to stabilize triplet carbenes kinetically to extent that they are able to survive under normal conditions, we attempt to protect the carbenic center of triplet diphenylcarbenes by introducing a series of substituents at the ortho position, and revealed that it is very effective on the stabilities of triplet diphenylcarbenes to introduce the big and unreactive substituents at ortho position. But this method has been limited that diazo compounds are used as precursor of carbenes and the preparation of diazo compound becomes more difficult as the bigger substituents are introduced in the ortho position. For this reason, the other approach, that the electronic (thermodynamic) effect of para substituents on the stabilities of triplet diphenylcarbenes, has been considered. To explore this effect, a series of triplet di(2,6 dimethylphenyl)carbenes (2) bearing symmetrical para strong electronic disubstituents have been generated by the irradiation of the corresponding diazo precursors and studied by means of electron paramagnetic resonance (EPR) spectroscopy. The zero field splitting parameters, D and E , were measured in matrices of different viscosities and were analyzed with molecular structures in terms of a scale of spin-delocalization substituent constants. And studied the stabilities of triplet di(2,6 dimethylphenyl)carbenes (2) by measuring the disappearance temperature of (2). Finally we have measured the life-time of the triplet di(2,6 dimethylphenyl)carbenes (2) by laser flash photolysis (LFP). It was showed that the triplet di(2,6 dimethylphenyl)carbene having stronger spin delocalized substituent have more line structure and show more stability.