The results herein demonstrate that the methods of circumscribing and the facile calculation of Hückel molecular orbital (HMO) eigenvalues by mirror-plane fragmentation have a broad application in the construction of carbon cluster series and the systematic study of trends in their electronic properties. In comparing open-ended nanotubes and their isomeric elongated fullerenes (bicapped nanotubes), we show that the former are more aromatic but the latter are more conjugated and that progressive elongation increases aromaticity and conjugation in both. Recursion equations that will allow one to obtain the eigenvalues to all 5-endcapped nanotubes are given.

A quantitative measure of the extent of conjugation is introduced. The number of Dewar resonance structures (DS) in a conjugated hydrocarbon quantitatively determines its extent of conjugation interaction. The greater the degree of conjugation the more stable is the conjugated hydrocarbon. The number of single bonds joining the exo-double bonds of a purely cross-conjugated hydrocarbon is equal to its number of Dewar resonance structures (DS). Polyene cross-conjugated hydrocarbons are minimally conjugated and possess only one classical structure with a succession of fixed single and exo-double bonds. There are three increasing levels of conjugation for systems with a single classical structure according to whether they are cross-conjugated, linear extended two-way conjugated, and ring-enhanced conjugated. Numerous analytical expressions have been derived. Our valence-bond (VB) approach involves studying the interrelationship of several well-known series of conjugated hydrocarbons having only a single classical structure, i.e., the number of Kekulé resonance structures is one (K = 1). This work provides a totally new perspective to the concept of conjugation.

A series of highly fluorescent p-phenylene–ethynylene π-conjugated oligomers (trimers and tetramers) with different chromophore substituents have been synthesized stepwise under oxygen-free Sonogashira conditions. The emission wavelengths range from 400 to 455 nm for the series. All four trimers and tetramers have visible blue emission under sunlight especially for the case of the pyrene-substituted trimer and tetramer. All oligomers also exhibit very high quantum yields (0.9–1.1), which suggest that these types of compounds could be used as blue-light-emitters.

The number of Kekulé resonance structures in a conjugated hydrocarbon is a measure of its singlet ground state, and its number of Dewar resonance structures is a measure of the triplet contribution to its ground state. We present a 2-dimensional organized study of rectangular benzenoids having both armchair and zigzag edges that play an important role in the electronic properties of nanographene patches and strips. Analytical expressions for the number of Dewar resonance structures (DS) for select series of rectangular benzenoid hydrocarbons are presented for the first time. An index of biradical character present (BRC) in polycyclic aromatic hydrocarbons is defined and illustrated. Biradical character is strongly influenced by zigzag edges and the presence of a diradical excised internal structure in polycyclic aromatic hydrocarbons.

Pauling’s valence-bond (VB) method for determining bond lengths is compared to ten recent literature experimental and theoretical results and is shown to give comparable results. His method only requires computation of the number of Kekulé (K) and Dewar structures (DS) of conjugated hydrocarbons. Both K and DS are obtained from the last two coefficients of the matching polynomial which is also used to obtain topological resonance energy (TRE). A molecular fragmentation method is given for determining DS of essentially disconnected polycyclic aromatic hydrocarbons (PAHs). Both Kekuléan alternant and nonalternant PAHs, including essentially disconnected and non-Kekuléan systems, have bond lengths that are easily determined by this method.

The first iodinated cyclopentadienone was isolated and its structure was confirmed by single crystal X-ray analysis. Based on this intermediate, the first direct C–C bond formation on cyclopentadienone ring was achieved. The photo induced intramolecular charge transfer of alkynylated cyclopentadienones was evaluated by solvent polarity effect on their electronic absorption spectra.

The systematics of fluoranthenoid/fluorenoid and indacenoid hydrocarbons is studied. Successive circumscribing a set of isomeric structures that result in a constant number of isomers at each circumscribing step gives what is called a constant-isomer series. Constant-isomer series have a repetitive isomer number pattern in which those series with the same isomer number have a one-to-one matching in topology among their membership. The general formulas of the matching constant-isomer sets of indacenoids are reproduced by \({{\rm C}_{{{4p}^{2}}{+1}}{\rm H}_{4p+1}}\) and \({{\rm C}_{{{4p}^{2}}{+4p+3}}{\rm H}_{4p+3}}\), respectively, by successively inputting p  =  1, 2, 3, . . ., and the general formula for the unique indacenoid constant-isomers is reproduced by \({{\rm C}_{{p^{2}}{+3p+4}}{\rm H}_{2p+4}}\). Similar general formulas for the fluoranthenoid/fluorenoid hydrocarbon constant-isomer series are also presented.

The 13C NMR spectra of over 24 tetracyclic triterpenoid derivatives have been structurally analyzed. The 13C NMR chemical shifts allow one to probe the steric topology of the rigid steroid skeleton and inductive effects of its substituents.Use of deuterium labeling in chemical shift assignment and B-ring aromatic terpenoids are also featured.

While the literature on coronoid hydrocarbons is comprehensively surveyed, new enumeration results on select coronoid classes are presented. The first examples of Kekuléan polycyclic (even-carbon) alternant hydrocarbons with doubly degenerate zero eigenvalues at the HMO level are identified. The parallelism between a molecule removed and the antimolecule hole left in formation of a graphite vacancy defect is elaborated. It is argued that the formation of a single carbon atom vacancy hole defect in graphite should be facile because it would entail a minimum electronic reorganization. These results are supported by a substantial amount of eigenvalue calculations. This work provides a unique overview for the class of coronoid hydrocarbons.

Recent development of the leapfrog operation in enumeration and understanding the chemical properties of benzenoid isomer sets having at least one synthesized representative is stressed. Some new enumeration results and correlations of the periodic table for the more stable total resonant sextet (TRS) benzenoid hydrocarbon subset [Table PAH6(sextet)] are presented.

The 13C-NMR spectra of well over 100 bile acid derivatives have been analyzed and summarized. A diagnostic γ-oxygen shielding effect has been identified.

The first iodinated cyclopentadienone was isolated and its structure was confirmed by single crystal X-ray analysis. Based on this intermediate, the first direct C–C bond formation on cyclopentadienone ring was achieved. The photo induced intramolecular charge transfer of alkynylated cyclopentadienones was evaluated by solvent polarity effect on their electronic absorption spectra.