| Description |
In this work 13C solid-state NMR and quantum mechanical studies of strained molecular systems are discussed. The chemical shift tensor values reported in this document were obtained using the FIREMAT method. Theoretical analyses of chemical shielding tensors were performed through the computer nodes operated by the Utah Center for High Performance Computing. Analyses were performed on sumanene, indenofluoranthene, tetrathiafulvalene, tetrathiafulvalene dimer, [2,2]paracyclophane, and 1,8-dioxa[8](2,7)pyrenophane. The FIREMAT data were fit using the TIGER data processing technique. TIGER provides a means to fit the FIREMAT data, accommodating its unique phase and relaxation characteristics. The details of the FIREMAT experiment are discussed in Chapter 1. The experimentally obtained chemical shift data were compared with calculated chemical shielding data. For these molecular systems, density functional theory was used along with the B3LYP exchange and correlation functionals. Multiple basis sets were used and relatively low errors are reported, between 2.0 ppm and 4.2 ppm. The errors reflect the difference between experimental and theoretical results. The relatively small errors are consistent with those of other polycyclic aromatic hydrocarbons (PAHs) and similar molecular systems. Chapter 2 discusses the three-dimensional aspect of tensor error analysis and how it is used in determining the errors associated with comparing two chemical shift tensors, i.e., theoretically derived and experimentally determined tensors. All error values reported and discussed in this dissertation are determined using this error analysis method. Molecular conformation may be explored by variation in chemical shift tensor principal values. The ring strain in curved polycyclic aromatic hydrocarbons can be associated with downfield shifts in the ?33 component of the chemical shift tensor. This is discussed in Chapters 3 and 5, as it relates to sumanene, indenofluoranthene, [2,2]paracyclophane, 1,8-dioxa[8](2,7)pyrenophane and how they compare to C60. Theoretical energy and NMR calculations, when compared with experimental solid-state NMR data, may also be used to refine X-ray crystal structures. This is useful in predicting the location of Hydrogen atoms in X-ray structures. Long bonding interactions are discussed in Chapter 4 regarding TTF and [TTF]22+ dimers. |
