Ground State of 1,6-Bridged [10] Annulenes:  Infrared and Raman Spectra and Density Functional Calculations

The infrared and Raman spectra of 1,6-methano[10]annulene and 1,6-epoxy[10]annulene, higher homologues of benzene with 10 π electrons, have been measured at room temperature in solution and in the solid phase. Density functional calculations using the B3-LYP functional and the 6-31G** basis set have been performed on the aforementioned molecules, on the 11,11-dicyano and 11,11-dimethyl derivatives of 1,6-methano[10]annulene, and on naphthalene. In general, the calculated molecular structures are in good agreement with X-ray data. The calculation of the vibrational frequencies and intensities of 1,6-methano[10]annulene and 1,6-epoxy[10]annulene allows a complete assignment of their spectrum in terms of bridge and ring modes. A correlation is attempted with the modes of naphthalene.