In this work, the substituent effect on the Se-H bond dissociation enthalpy (BDE) for benzeneselenol and ten para-substituted benzeneselenols was investigated. The set of various electron-donating and electron-withdrawing substituents was used. The gas-phase bond dissociation enthalpies were calculated using B3LYP/6-311++G ** method. Obtained trends were compared with those found for para-substituted phenols and thiophenols for the same set of substituents. While the BDE = f(σ p ) dependences

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... r phenols and thiophenols exhibit very good linearity, for benzeneselenols, the linearity is rather insuffi cient. It was found for oxygen, sulphur and selenium that the larger the atom is, the weaker the substituent induced changes in corresponding BDE values are. It has been also observed that the larger the atom, the smaller corresponding BDEs.