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- In organic chemistry, the term 2-norbornyl cation (or 2-bicyclo[2.2.1]heptyl cation) describes one of the three carbocations formed from derivatives of norbornane. Though 1-norbornyl and 7-norbornyl cations have been studied, the most extensive studies and vigorous debates have been centered on the exact structure of the 2-norbornyl cation. The 2-norbornyl cation has been formed from a variety of norbornane derivatives and reagents. First reports of its formation and reactivity published by Saul Winstein sparked controversy over the nature of its bonding, as he invoked a three-center two-electron bond to explain the stereochemical outcome of the reaction. Herbert C. Brown challenged this assertion on the grounds that classical resonance structures could explain these observations without needing to adapt a new perspective of bonding. Both researchers' views had its supporters, and dozens of scientists contributed ingeniously designed experiments to provide evidence for one viewpoint or the other. Over time, the dispute became increasingly bitter and acrimonious, and the debate took on a personal or ad hominem character. Evidence of the non-classical nature of the 2-norbornyl cation grew over the course of several decades, mainly through spectroscopic data gathered using methods such as nuclear magnetic resonance (NMR). Crystallographic confirmation of its non-classical nature did not come until 2013. Although most chemists now agree that 2-norbornyl cation itself is non-classical, it is also widely recognized that the energetic landscape for carbocations tends to be "flat", with many potential structures differing only minutely in energy. Certainly, not all bicyclic carbocations are non-classical; the energy difference between classical and non-classical structures is often delicately balanced. Thus, certain alkyl-substituted 2-bicyclo[2.2.1]heptyl cations are now known to adopt classical structures. The nature of bonding in the 2-norbornyl cation incorporated many new ideas into the field’s understanding of chemical bonds. Similarities can be seen between this cation and others, such as boranes. (en)
- 非经典碳正离子或非经典离子是有機化學中的一種碳正离子，含有三中心两电子键，σ键的电荷不只定域在一个原子上，「非经典离子」一詞一開始是由J.D. Roberts在1951年用來描述环丁烷正離子，但此在1949年化學家Saul Winstein就用這種離子解釋降冰片基化合物的反應性。 上述提及的化合物是exo-降冰片基和的化合物（下圖中標示1）及其endo異構物（下圖中標示3），而其反應是在乙酸中和乙酸鉀進行酰化反应。重要的是在亲核取代反应中二種異構物都產生了相同的生成物（下圖中標示2），而exo构型反應的反應速率是endo构型反應或是環己烷類似反應的350倍。 (zh)
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- 非经典碳正离子或非经典离子是有機化學中的一種碳正离子，含有三中心两电子键，σ键的电荷不只定域在一个原子上，「非经典离子」一詞一開始是由J.D. Roberts在1951年用來描述环丁烷正離子，但此在1949年化學家Saul Winstein就用這種離子解釋降冰片基化合物的反應性。 上述提及的化合物是exo-降冰片基和的化合物（下圖中標示1）及其endo異構物（下圖中標示3），而其反應是在乙酸中和乙酸鉀進行酰化反应。重要的是在亲核取代反应中二種異構物都產生了相同的生成物（下圖中標示2），而exo构型反應的反應速率是endo构型反應或是環己烷類似反應的350倍。 (zh)
- In organic chemistry, the term 2-norbornyl cation (or 2-bicyclo[2.2.1]heptyl cation) describes one of the three carbocations formed from derivatives of norbornane. Though 1-norbornyl and 7-norbornyl cations have been studied, the most extensive studies and vigorous debates have been centered on the exact structure of the 2-norbornyl cation. The nature of bonding in the 2-norbornyl cation incorporated many new ideas into the field’s understanding of chemical bonds. Similarities can be seen between this cation and others, such as boranes. (en)
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- 2-Norbornyl cation (en)
- 非经典碳正离子 (zh)
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