Department of Chemistry, Virginia Commonwealth University, 1001 W. Main Street, Richmond, Virginia 23284, United States.
J Am Chem Soc. 2011 Mar 16;133(10):3381-9. doi: 10.1021/ja1071493. Epub 2011 Feb 22.
Thermodynamic stabilities of 92 carbenes, singlets and triplets, have been evaluated on the basis of hydrogenation enthalpies calculated at the G3MP2 level. The carbenes include alkyl-, aryl-, and heteroatom-substituted structures as well as cyclic 1,3-diheteroatom carbenes. Over a wide energy range, a good correlation is seen between the singlet-triplet gaps and the hydrogenation enthalpies of the singlets, but there are some clear outliers, which represent cases where the triplet has unusual stability or instability. By use of hydrogenation enthalpies, separate carbene stabilization enthalpy scales (CSEs) have been developed for singlets and triplets, and these highlight structural features that affect the stability of each. The treatment also allows estimates of aromaticity in cyclic carbenes. In this way, imidazol-2-ylidene is estimated to have an aromatic stabilization energy of about 20 kcal/mol.
基于 G3MP2 水平计算的氢化焓，评估了 92 个卡宾、单线态和三线态的热力学稳定性。这些卡宾包括烷基、芳基和杂原子取代结构以及环状 1,3-杂原子卡宾。在很宽的能量范围内，单线态-三线态能隙与单线态的氢化焓之间存在很好的相关性，但也有一些明显的异常值，这代表了三线态具有异常稳定性或不稳定性的情况。通过使用氢化焓，为单线态和三线态分别开发了单独的卡宾稳定焓标度（CSE），这些标度突出了影响每种稳定性的结构特征。该处理方法还允许估计环状卡宾中的芳香性。通过这种方式，咪唑-2-亚基被估计具有约 20 kcal/mol 的芳香稳定能。
