Out-of-plane deformability of aromatic systems in naphthalene, anthracene and phenanthrene

The results of computational studies using the MP2/cc-pvdz approximation reveal high conformational flexibility of aromatic systems in naphthalene, anthracene and phenanthrene. In the gas phase all of these molecules possess two different types of out-of-plane deformations which are associated with the distortion of the benzene ring coplanarity and out-of-plane deformation of the separated rings. A change in the relevant C–C–C–C torsion angles of 158 results in an energy increase of less than 1.25 kcal/mol. Therefore, in every unit amount of time, more than 50% of the molecules have significant non-planar geometry. It is demonstrated that the energy of out-of-plane deformations correlates well with changes in the degree of aromaticity of the conjugated system of whole molecules as well as specific rings. q 2004 Elsevier B.V. All rights reserved