The Vibration Frequencies of [6] Cyclacenes (Linear, Angular and Angular-Chiral) Monoring Molecules

Abstract

The (3N-6) vibration frequencies and IR-absorption intensities of [6] Cyclacene  (linear, angular and angular-chiral) monoring molecules were calculated applying Density Functional Theory (DFT) of the type (B3LYP) and a Gaussian basis (6-311G) method. Comparison of the results showed that, similar to the polyaromatic hydrocarbons, the following relations hold: n_symmetricCH str.  > n_asymmetric CH str.   and, n_symmetric CC str.  > n _asymmetric CC str.  i. e., the following relation hold too,n_symmetric. CC str.(axial.) > n_asymmetric. CC str.(axial) > n_asymmetric. CC str. (circumferential) in the linear molecule, where axial are the vertical C-C_a bonds (annular bonds) in the rings and circumferential C-C_c are the outer ring bonds.The relation for the C-Cstr. is reversed in the angular and the angular-chiral molecules, since the C-Ca bonds are converted to C-Cc bonds in the angular and angular-chiral cyclacenes. The results include the assignment of all puckering, breathing and clock-anticlockwise bending vibrations. They allow a comparative view of the charge density at the carbon atoms too.