We investigate the minimum-energy path for the rotation of formal C=N double bonds in molecules with guanidine-like substructures as present in the chemical class of neonicotinoids. The transitions between the E- and Z-isomers of several neonicotinoids using scans of the torsional potential energy hypersurfaces are quantified at the DFT-level of theory. The validity of using this ansatz is checked by single-point CCSD(T) calculations for model systems like nitroguanidine. A combined approach of theory and experiment permits to unambiguously identify the relevant isomers present at ambient conditions. As an example, MP2-GIAO predictions of the NMR spectra of E- and Z-Clothianidin are experimentally confirmed by low-temperature NMR-experiments identifying for the first time the hitherto unknown Z-Isomer of Clothianidin.

我们研究了新烟碱类化合物中存在的类胍亚结构分子中形式 C=N 双键旋转的最小能量路径。使用扭转势能超曲面扫描的几种新烟碱类的E和Z异构体之间的转变在理论的 DFT 级别进行量化。使用此 ansatz 的有效性通过单点 CCSD(T) 计算来检查模型系统（如硝基胍）。理论和实验相结合的方法可以明确识别环境条件下存在的相关异构体。例如，MP2-GIAO 对E - 和Z的核磁共振谱的预测-Clothianidin 通过低温 NMR 实验得到实验证实，首次鉴定了迄今为止未知的Clothianidin 的Z -异构体。