Prototropic tautomerism of the addition products of N-heterocyclic carbenes to CO2, CS2, and COS

  • Ibon AlkortaEmail author
  • José Elguero
Original Research


The energies of 62 minima and 6 transition states have been calculated with the M06-2x functional and the aug-cc-pVDZ basis set. They correspond to carbenes and neutral molecules related to the products obtained by addition of N-heterocyclic carbenes (NHCs) to CO2, CS2, and COS. The NHCs belong to two “classical” NHCs (imidazoles and benzimidazoles) and one “remote” NHC (pyrazole). Several of these structures in the same series are related by prototropic tautomerism. To compare these calculated energies with experimental X-ray structures, solvation effects by water, calculated with a continuous model (PCM), as well as some dihydrates and dimers, have also been calculated.


NHC Imidazoles Benzimidazoles Pyrazoles Carboxylic acids X-ray structures 



The authors would like to thank the CTI (CSIC) for their continued computational support.

Funding information

This work was carried out with the financial support from the Ministerio de Ciencia, Innovación y Universidades (Project No. PGC2018-094644-B-C22) and Comunidad Autónoma de Madrid (P2018/EMT-4329 AIRTEC-CM).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

11224_2019_1381_MOESM1_ESM.docx (45 kb)
ESM 1 (DOCX 45 kb)


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© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Instituto de Química Médica, CSICMadridSpain

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