NMR Spectroscopic and quantum chemical characterization of the (<i>E </i>)− and (<i>Z </i>)− isomers of the penta-1,3-dienyl-2-cation
作者:Hans-Ullrich Siehl、Thomas Müller、Jürgen Gauss
DOI:10.1002/poc.662
日期:2003.8
this type of carbocation. Inclusion of electron correlation, however, allows an unequivocal assignment of the spectra of the Z- and E-isomers. The mean deviation between experimental and calculated NMR chemical shifts at the CCSD(T) level is 1.8 and 2.0 ppm for (Z)- and (E)-1, respectively. The dienyl cations (E/Z)-1 are the smallest vinyl cations ever generated as persistent species in superacidic solutions
戊-1,3-二烯基-2-阳离子(1)的(E )-和(Z )-异构体的稀溶液是由4-氯-1,2-戊二烯(2)与SbF 5在使用高真空共冷凝技术在-135°C下进行SO 2 ClF / SO 2 F 2。将两种异构体的混合物的实验NMR光谱与量子化学13进行了比较使用MP2 / tzp几何结构在HF-SCF,MP2,CCSD和CCSD(T)级别进行C NMR化学位移计算。使用包括原子规在内的原子规(GIAO),以碳的tzp基(9s5p1d / 5s3p1d)和氢的dz基(4s / 2s)进行量子化学位移计算。与实验观察到的化学位移相比,烯丙基型共振系统带正电荷的碳原子的HF-SCF计算值显着偏离,显示高达40 ppm的去屏蔽值。因此,HF-SCF方法不足以令人满意地预测此类碳正离子中的屏蔽张量。但是,包含电子相关性可以明确分配Z-和E的光谱-异构体。对于(Z)-和(E)-1,在CCSD(T)含