As determined by X-ray crystallography, isoxazol-5(4H)-one derivatives 12–19 feature dihedral angles around the exocyclic C4=C6 double bonds of 26–90°. In the most highly twisted bis-tert-butylamino derivatives 18 and 19, the C4–C6 bonds are essentially single bonds. Density functional theory calculations at the B3LYP/6-31G(d) level with inclusion of a simulated solvent field, which helps stabilize
如通过X射线晶体学,
异恶唑-5-(4-确定ħ) -酮衍
生物12 - 19围绕环外C4特征二面角=的26-90°C6双键。在高度扭曲的双叔丁基
氨基衍
生物18和19中,C4-C6键本质上是单键。在B3LYP / 6-31G(d)级别上的密度泛函理论计算,包括模拟的溶剂场,有助于稳定两性离子结构,与实验晶体学数据非常吻合。观察到键长与计算出的π/π*轨道占有商之间具有良好的相关性。还观察到扭曲角和电荷分离之间的良好相关性,该相关性是通过在
异恶唑酮部分上计算出的负电荷测得的。低障碍绕扭转环外双键C4 = C6化合物在13,20,和21(Δ ģ ‡ = 15-16千卡摩尔-1(63-67千焦耳摩尔-1))是通过动态1 H NMR聚结测量确定的。估计17的旋转势垒小于10 kcal mol –1。化合物10和18的旋转势垒经计算为〜8 kcal mol –1。