Here we show that amides of bicyclic 7-azabicyclo[2.2.1]heptane are intrinsically nitrogen-pyramidal. Single-crystal X-ray diffraction structures of some relevant bicyclic amides, including the prototype N-benzoyl-7-azabicyclo[2.2.1]heptane, exhibited nitrogen-pyramidalization in the solid state. We evaluated the rotational barriers about the amide bonds of various N-benzoyl-7-azabicyclo[2.2.1]heptanes in solution. The observed reduction of the rotational barriers of the bicyclic amides, as compared with those of the monocyclic pyrrolidine amides, is consistent with a nitrogen-pyramidal structure of 7-azabicyclo[2.2.1]heptane amides in solution. A good correlation was found between the magnitudes of the rotational barrier of N-benzoyl-7-azabicyclo[2.2.1]heptanes bearing para-substituents on the benzoyl group and the Hammett's sigma(p)(+) constants, and this is consistent with the similarity of the solution structures. Calculations with the density functional theory reproduced the nitrogen-pyramidal structures of these bicyclic amides as energy minima. The calculated magnitudes of electron delocalization from the nitrogen nonbonding n(N) orbital to the carbonyl pi orbital of the amide group evaluated by application of the bond model theory correlated well with the rotational barriers of a variety of amides, including amides of 7-azabicyclo[2.2.1]heptane. The nonplanarity of the amide nitrogen of 7-azabicyclo[2.2.1]heptanes would be derived from nitrogen-pyramidalization due to the CNC angle strain and twisting of the amide bond due to the allylic strain.

中文翻译：

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7-氮杂双环[2.2.1]庚烷酰胺中酰胺基团平面性的评价。溶液中的低酰胺键旋转屏障

在这里，我们表明双环 7-氮杂双环 [2.2.1] 庚烷的酰胺本质上是氮锥体。一些相关双环酰胺的单晶 X 射线衍射结构，包括原型 N-苯甲酰基-7-氮杂双环 [2.2.1] 庚烷，在固态下表现出氮锥体化。我们评估了溶液中各种 N-苯甲酰基-7-氮杂双环 [2.2.1] 庚烷的酰胺键的旋转势垒。与单环吡咯烷酰胺相比，观察到的双环酰胺旋转势垒的降低与溶液中 7-氮杂双环 [2.2.1] 庚烷酰胺的氮-锥体结构一致。发现在苯甲酰基上带有对位取代基的 N-苯甲酰基-7-氮杂双环[2.2.1]庚烷的旋转势垒的大小与哈米特'之间存在良好的相关性 s sigma(p)(+) 常数，这与解结构的相似性一致。使用密度泛函理论的计算再现了这些双环酰胺的氮-锥体结构作为能量最小值。通过应用键模型理论评估的从氮非键合 n(N) 轨道到酰胺基团的羰基 pi 轨道计算的电子离域量与各种酰胺的旋转势垒很好地相关，包括 7-氮杂双环的酰胺[2.2.1]庚烷。7-氮杂双环[2.2.1]庚烷的酰胺氮的非平面性源于由于CNC角应变引起的氮锥体化和由于烯丙基应变引起的酰胺键扭曲。使用密度泛函理论的计算再现了这些双环酰胺的氮-锥体结构作为能量最小值。通过应用键模型理论评估的从氮非键合 n(N) 轨道到酰胺基团的羰基 pi 轨道计算的电子离域量与各种酰胺的旋转势垒很好地相关，包括 7-氮杂双环的酰胺[2.2.1]庚烷。7-氮杂双环[2.2.1]庚烷的酰胺氮的非平面性源于由于CNC角应变引起的氮锥体化和由于烯丙基应变引起的酰胺键扭曲。使用密度泛函理论的计算再现了这些双环酰胺的氮-锥体结构作为能量最小值。通过应用键模型理论评估的从氮非键合 n(N) 轨道到酰胺基团的羰基 pi 轨道计算的电子离域量与各种酰胺的旋转势垒很好地相关，包括 7-氮杂双环的酰胺[2.2.1]庚烷。7-氮杂双环[2.2.1]庚烷的酰胺氮的非平面性源于由于CNC角应变引起的氮锥体化和由于烯丙基应变引起的酰胺键扭曲。通过应用键模型理论评估的从氮非键合 n(N) 轨道到酰胺基团的羰基 pi 轨道计算的电子离域量与各种酰胺的旋转势垒很好地相关，包括 7-氮杂双环的酰胺[2.2.1]庚烷。7-氮杂双环[2.2.1]庚烷的酰胺氮的非平面性源于由于CNC角应变引起的氮锥体化和由于烯丙基应变引起的酰胺键扭曲。通过应用键模型理论评估的从氮非键合 n(N) 轨道到酰胺基团的羰基 pi 轨道计算的电子离域量与各种酰胺的旋转势垒很好地相关，包括 7-氮杂双环的酰胺[2.2.1]庚烷。7-氮杂双环[2.2.1]庚烷的酰胺氮的非平面性源于由于CNC角应变引起的氮锥体化和由于烯丙基应变引起的酰胺键扭曲。