The Se–H bond of benzeneselenols (ArSe-H): Relationship between bond dissociation enthalpy and spin density of radicals

Abstract

Bond dissociation enthalpies (BDE) of benzeneselenol (ArSe-H) and its para and meta-substituted derivatives are calculated using the (RO)B3LYP/6-311++G(2df,2p)//(U)B3LYP/6-311G(d,p) procedure. The computed BDE(Se–H)=308±8kJ/mol for the parent PhSe-H is significantly smaller than the experimental value of 326.4±16.7kJ/mol [Kenttamaa and coworkers, J. Phys. Chem. 100 (1996) 6608] but larger than a previous value of 280.3kJ/mol [Newcomb et al., J. Am. Chem. Soc. 113 (1991) 949]. The substituent effects on BDE’s are analyzed in terms of a relationship between BDE(Se–H) and Mulliken atomic spin densities at the Se radical centers of ArSe (π radicals). Good correlations between Hammett’s substituent constants with BDE(Se–H) are established. Proton affinity and ionization energy amount to PA(C6H5SeH)=814±4kJ/mol and IE(C6H5SeH)=8.0±0.1eV. IEs of the substituted benzeneselenols are also determined. Calculated results thus suggest that 4-amino-benzeneselenol derivatives emerge as efficient antioxidants.