The mono- and di-silanaphthalene: structure, properties, and aromaticity

The electronic structure and properties of the mono-silanaphthalene and di-silanaphthalene series have been investigated using basis set of 6-31G** and hybrid density functional theory. Basic measures of aromatic character derived from structure, molecular orbitals, a variety of magnetic criteria (magnetic isotropic and anisotropic susceptibilities) are considered. Energetic criteria suggest that NSi2 and, and NSi1,2 enjoy conspicuous stabilization. However, by magnetic criteria, these systems are among the least aromatic of the family: within their isomer series, NSi8,9 and NSi9 are the most aromatic using magnetic criteria. Natural bond orbital (NBO) analysis method was performed for the investigation of the relative stability and the nature of the C9-C10 bond in naphthalene, mono-sialnaphthalene and di-silanaphthalene compounds. The results explained that how the p character of natural atomic hybrid orbital on C9 and C10 (central bond) is increased by the substitution of the C9 and C10 by Si. The NBO analysis of donor-acceptor (bond-antibond) interactions resulted in increasing of occupancy of the localized σC9-C10 orbital of the idealized Lewis structure, decreasing of occupancy of sp C9-C10 of the non-Lewis orbital, and also their subsequent impact on molecular stability and geometry (bond length) along with the resulting p character of the corresponding carbon NHO of s bond orbital. Actually, the results suggested that in these compounds, the C9-C10 bond lengths are closely controlled by the p character of these hybrid orbitals and also by the nature of C-Si bonds. The magnitude of the molecular stabilization energy associated to delocalization from σC9-C10 to σC9−C10* bond orbital were also quantitatively determined.