| Abstract
| - Density functional theory (B3LYP) calculationswere performed to examine the effect of Si substitution onthe aromaticity of some polycyclic hydrocarbons usinggeometric criterion (HOMA), isodesmic isomerization reactions, homodesmotic equations, NICS values, chemical hardness, and out-of-plane distortive tendencies. The HOMAvalues are lower and the NICS values are higher in the Si-substituted rings compared to those in the hydrocarboncounterpart, whereas the homodesmotic equations predictlittle loss of aromaticity upon Si replacement in polycylicsystems. The chemical hardness values decrease and the out-of-plane distortive tendency increases upon silicon substitution. The relative energies of the positional isomers and thecausative factors are analyzed. The high reactivity of somesilaaromatics toward dimerization is explained based onlocal softness indices.
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