Polycalicenes are novel nonbenzenoid aromatic hydrocarbons made from calicene subunits. A host of related polycalicenes are possible by varying the number of calicenes and the bonding motif of the calicenes (e.g. head-to-tail versus head-to-head). Polycalicenes might posses interesting and useful electrical, magnetic, and optical properties. Especially intriguing is that while calicene has never been synthesized, bicalicene 2, where two calicenes are bonded head-to-tail, has been synthesized by Yoshida et al. and found to be aromatic despite having a peripheral 16 ð electron count. This study details a computational investigation of the aromaticity of some planar polycalicenes using the nucleus independent chemical shift (NICS) criterion of aromaticity. NICS values were calculated with HF/6-31+G(d,p) and B3LYP/6-31+G(d,p). Bicalicene 3, where two calicenes are bonded head-to-head, was shown to have a triplet ground state which required the calculation of NICS values using UB3LYP/6-31+G(d,p). Also, the aromaticities of some “belted” polycalicenes were evaluated using NICS values calculated at 6-31G(d,p). The smaller basis set was used due to the increasing number of basis functions for the larger “belted” polycalicenes. In addition, the electronic ground and excited states of the planar polycalicenes were also calculated. The electronic ground states were assigned using HF/6-31+G(d,p) and B3LYP/6-31+G(d,p). CCSD(T)/6-31G(d,p) calculations were used to confirm assignments. The electronic excited states were calculated using time dependent density functional theory (TDDFT) and B3LYP/6-31+G(d,p). Recently, the reliability of the NICS criterion was questioned when it was claimed NICS found the cyclopropenyl anion to be aromatic. One part of this study details the examination of this claim and concluded that the earlier work was in error. The error was proven to arise from the failure to employ diffuse basis functions in the earlier work.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-1078 |
| Date | 02 May 2009 |
| Creators | Collier, Willard |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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