Studies on Electronic Effects on the Singlet-Triplet Gap of Aryl-C4H3Si

2013 Asian Journal of Chemistry  
Divalent carbenes and their analogues are strongly reactive 1 . The cyclic completely conjugated species are important in the chemistry of divalent carbene intermediates 2 . These divalent structures were formerly described in terms of the Huckel 4n + 2 rule 3 . However, non-planar isomers are found energy minima for most of these singlet cyclic conjugated carbenes through semi-empirical studies 4 . The isolation of the stable five membered cyclic conjugated carbene is firstly reported by
more » ... go et al. 5 and then Su and Chu 5 . Since most of divalent carbenes and their analogues are unstable, theoretical calculation was required for analysis of their properties. In continuation of our studies 2,6 , in this manuscript, the singlettriplet gap energies were studied on Ar-C4H3Si (G = -NH2, -OH, -CH3, -F, -Cl, -Br, -H, -CF3 and -NO2). Full geometry optimizations of Ar-C4H3Si were carried out by density functional theory, DFT, method using 6-311++G** basis set of the GAUSSIAN 98 program 7-9 (Scheme-I). To find a global minimum on a specific surface, all possible conformations of the given species were examined through scanning the specific dihedral angles at B3LYP/6-311++G** level. All calculations were carried out for gas phase at 298 K temperature and 1 atm pressure. The thermal energies (E), enthalpies (H), Gibbs free energies (G) and their gap energies between singlet (s) and triplet (t) states including ∆Es-t, ∆Hs-t and ∆Gs-t of Ar-C4H3Si (G = -NH2, -OH, -CH3, -F, -Cl, -Br, -H, -CF3 and -NO2) were calculated at B3LYP/6-311++G** level of theory (Scheme-I and Table-1). The gap free energies, ∆Gs-t, for various substituents were changed in the followed order: -Br > -CF3 > -NO2 > -H > -Cl > -CH3 > -F > -NH2 > -OH.
doi:10.14233/ajchem.2013.14268 fatcat:3xblen4hsngxpotxvz7r3rqq2q