2011/02/22 by Scott Gronert, James R. Keeffe, Rory A. More O‘Ferrall · 1 citation
Chemistry · #N-Heterocyclic Carbenes in Organic and Inorganic Chemistry #Synthesis and Properties of Aromatic Compounds #Chemical Reactions and Mechanisms
paper · doi:10.1021/ja1071493
openalex publication_date 2011/02/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/16
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.