Abstract
The electronic structure of HOCN, HSCN, HNCO, and HNCS molecules and [OCN]− and [SCN]− anions has been studied by ab initio calculations at HF/6-31G(d), HF/6-31G(d, p), MP2/6-31G(d)//HF/6-31G(d), and MP2/6-31G(d, p)//HF/6-31G(d, p) levels of theory. The HNCO and HNCS molecules are shown to have higher thermodynamic stability than HOCN and HSCN, respectively. The protolyte strength series are substantiated: HSCN > HOCN, HNCS > HNCO, HOCN > HNCO, HSCN > HNCS. Computations including electron correlation [MP2/6-31G(d)//HF/6-31G(d) and MP2/6-31G(d, p)//HF/6-31G (d, p)] reproduce the general sequence of proton-donor properties: HSCN > HOCN > HNCS > HNCO, which coincides with the hydrophobicity series for the compounds. The relative proton-donor capacity of these acids in water solutions is generally governed by the electronic structure and by the size of their molecules and [OCN]− and [SCN]− anions, but not by medium effects.
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Original Russian Text Copyright © 2005 A. N. Pankratov and S. S. Khmelev
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Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 416–421, May–June, 2005.
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Pankratov, A.N., Khmelev, S.S. Protolytic properties of cyanic and thiocyanic acids and their isoforms. J Struct Chem 46, 404–408 (2005). https://doi.org/10.1007/s10947-006-0117-y
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DOI: https://doi.org/10.1007/s10947-006-0117-y