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Updated: Aug 16, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Proton affinities of N-heterocyclic carbene super bases
Hao Chen1, Dina R Justes, R Graham Cooks
1Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
Abstract:
The gas-phase proton affinity of the N-heterocyclic carbene, 1-ethyl-3-methylimidazol-2-ylidene, was determined to be 251.3 +/- 4 kcal/mol using the kinetic method, a value which makes the carbene one of the strongest bases reported thus far. Density functional theory calculations have been carried out at the B3LYP/6-31+G(d) level to compare the high experimental value with that estimated theoretically. Experimental results also show that two other N-heterocyclic carbenes with larger substituents have even higher proton affinities. [structure: see text]
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