depends upon the polarity of the solvent. This allowed us to assign the anti structure, which has a null dipole moment, to the least retained isomer. The free energy of activation (DeltaG) for the interconversion was found to be 22.5 kcal mol(-)(1), a value high enough for identifying these species as configurational isomers. When less hindered derivatives, also having two RCO (R = Pr(i), Et, Me) substituents
由1,4-双(2,2-二甲基丙酰基)二氢
呋喃(2e)中Ar-C(O)Bu(t)单键的有限旋转引起的正交顺式和反式异构体已通过制备层色谱。在溶液中,它们达到平衡,其中反-反比例取决于溶剂的极性。这使我们可以将具有零偶极矩的反结构分配给保留最少的异构体。发现用于相互转化的活化自由能(DeltaG)为22.5 kcal mol(-)(1),该值足够高,可以识别这些物种为构型异构体。当检查受阻较小的衍
生物(在杜蕾烯部分的1,4位上也有两个RCO(R = Pr(i),Et,Me)取代基)时,只能通过低温检测顺式和反式NMR光谱学。