Total carbo-Mer of Benzene, Its carbo-Trannulene Form, and the Zigzag Nanotube Thereof

Abstract

The total carbo-mer of benzene, hexaethynyl carbo-benzene C30H6, has been calculated at the B3PW91/6-31G** level. Its geometrical and magnetic characteristics are compared with those of the C18H6 partial carbo-mers, unsubstituted carbo-benzene, and hexaethynylbenzene. The carbo-[6]trannulene isomer is found to exist as a minimum on the singlet spin state potential energy surface (PES) and is 65.6 kcal.mol(-1) higher in energy than hexaethynyl-carbo-benzene. In the former, a strong cyclic electron delocalization is evidenced from the root-mean-square deviation (rms) of the ring bond lengths and the NICS value computed at the centroid of the trannulene ring. As an alternative to the graphene sheet wrapping process traditionally used to illustrate the construction of carbon nanotubes, a dehydrocoupling-stacking process is invoked for the construction of zigzag nanotubes from trannulene bricks. The process is applied to the carbo-[6]trannulene brick to generate a novel type of acetylene-expanded carbon nanotube, which is a polymer of primitive C60 segments. A C60H6 carbo-meric equivalent of a cyclacene belt is first considered. Two such segments are then formally dehydrocoupled to generate a cylindrical (C60)2H6 molecule, the central part of which is assumed to be a relevant model for the infinite nanotube. Axial and sectional electron delocalization inside the tube models is discussed on the basis of bond length analysis, NICS values, pi MO analysis, and singlet-triplet state energy gap. The capping of the C120 cyclinder is finally addressed by use of carbo-[3]radialenic units.