The γ-dissociations of 3-substituted bicyclo[1.1.1]pent-1-yl radicals and cyclobutyl radicals were investigated by abinitio SCF MO (HF, MP2, MP3 and MP4/6â31G*) and density functional methods (B3LYP/6â31G*). The transition states were found to resemble the product alkyl radical and [1.1.1]propellane or bicyclo[1.1.0]butane. Calculated endothermicities and energy barriers were comparatively low for loss of the t-butyl radical from the 3-t-butylbicyclo[1.1.1]pent-1-yl radical, which suggested that this dissociation would be significant under laboratory conditions. The dissociation was verified experimentally by means of the reaction of 1-iodo-3-t-butylbicyclo[1.1.1]pentane with tributyltin hydride. Arrhenius parameters for this dissociation were determined by end product analysis. The SCF MO and density functional calculations resulted in much higher endothermicities and energy barriers for γ-dissociations of cyclobutyl radicals, hence neither the formation of bicyclo[1.1.0]butane nor alkyl radical addition to this bicyclic compound was predicted to be important.
                                    通过从头算SCF MO(HF、MP2、MP3和MP4/6-31G*)和密度泛函方法(B3LYP/6-31G*),研究了3-取代双环[1.1.1]戊-1-基自由基和
环丁基自由基的γ-解离。过渡态被发现类似于产物烷基自由基和[1.1.1]螺旋烷或双环[1.0.0]
丁烷。计算得出,从3-叔丁基双环[1.1.1]戊-1-基自由基中失去叔丁基自由基的反应热和能垒相对较低,这表明在实验室条件下这种解离将十分显著。通过1-
碘-3-叔丁基双环[1.1.1]
戊烷与三
丁基锡氢的反应,实验验证了这一解离。通过最终产物分析确定了该解离的阿伦尼乌斯参数。SCF MO和密度泛函计算结果表明,
环丁基自由基的γ-解离反应热和能垒要高得多,因此预测
双环[1.1.0]丁烷的形成或烷基自由基对该
双环化合物的加成都不重要。