Comparison of the Vibration Frequencies of [6] Cyclacene (Zigzag, Armchair and Chiral) Monoring Molecules


AbstractThe (3N-6) vibration frequencies and IR-absorption intensities of [6] Cyclacene (zig zag, armchair and 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:nsym. CH str. > n asym. CH str. and, nsym. CC str. > n asym. CC str. i. e., nsym. CC str.(axial.) > nasym. CC str.(axial) > nasym. CC str.(circumferential) in the zigzag molecule, where axial are the vertical C-Ca bonds (annular bonds) in the rings and circumferential C-Cc are the outer ring bonds. The relation for the C-C str. is reversed in the armchair and the chiral molecules, since the C-Ca bonds are converted to C-Cc bonds in the armchair and 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.