Abstract
The electron shells of imidazole, pyrazole, and their ethynyl derivatives were calculated by the CNDO/2 method (complete neglect of differential overlap). The dipole moments, ionization potentials, and energies of heterolytic cleavage of the CH bonds of the ethynyl groups were calculated. The results are compared with the experimental data on the reactivities and acidities. The ethynyl substituent is a weak electron acceptor. The donor capacity of the ring correlates with the charges on the corresponding carbon atoms. The 4 and 5 positions of imidazole constitute an exception to this. The energy of heterolytic cleavage of the CH bond decreases as the electronic charge on the ethynyl group increases.
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Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 821–825, June, 1975.
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Schatnev, P.V., Shvartsberg, M.S. & Bernshtein, I.Y. Electron-density distribution and reactivities of ethynylimidazoles and -pyrazoles. Chem Heterocycl Compd 11, 718–722 (1975). https://doi.org/10.1007/BF00959971
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DOI: https://doi.org/10.1007/BF00959971