Aromatička svojstva potpunih benzenoidnih ugljikovodika

We consider a family of structurally closely related fully-benzenoid hydrocarbons of increasing number of fused benzene rings. Local and global aromatic properties of such molecules are investigated with a particular interest in investigating the role of the finite size of such molecules in modelling the high-polymer or even graphite. An interesting alternation of local properties for benzene rings in a similar environment was observed.Razmatrana je skupina strukturno vrlo sličnih potpunih benzenoidnih ugljikovodika. Studirana su lokalna i globalna svojstva ovih molekula, a naročita je pažnja posvećena ulozi konačne veličine studiranih molekula u modeliranju benzenoidnih polimera ili čak grafita. Opažena je interesantna pojava da lokalna svojstva benzenskih prstenova alterniraju u sličnom okolišu, iako razlike u veličinama opadaju rastom veličine molekule

The Equivalent Bond Orbital Model Revisited: I. Orbitals, Orbital Energies and PE Spectra of Saturated Hydrocarbons

The EBO model, originally proposed by Lennard-Jones and Hall, many years ago, is reexamined using localized orbitals (LMO) stemming from SCF ab initio calculations. It is found that only a· limited set of matrix elements is needed to build a Fock matrix F, (in localized basis) the diagonalization of which yields orbital energies of sufficient precision for use in the assignment of photoelectron spectra within Koopmans e1pproximation. The model so obtained can be easily parametrized with respect to a given calibration set, if the relative size of the off-diagonal elements suggested by the ab initio calculation is conserved. It is argued that such EBO models, which are essentially of Hiickel-type, Cl\u27!\u27e necessary for the qualitative or semi-quantitative rationalization of experimental and theoretical data (from more sophisticated calculations). Some of the more important limitations of LMO-based EBO models ctre discussed

Hybridization in Highly Strained Small Ring Hydrocarbons. I. Tricyclo- and Tetracyclopropylidene

The hybridization in tricyclopropylidene and tetracyclopropylidene has been calculated by the method of maximum overlap. The results show that the hybrids describing the central ring have more s character than those in cyclopropane and cyclobutane: sp3·02 and sp3·31 as compared to sp3·86 and sp3·47 respectively. Consequently the central bonds in the two molecules investigated . are stabilized by the cyclopropyl substitutions. An interesting comparison between the maximum overlap hybridization and hybridization based on more elaborated calculations is made

π-Conjugated Macrocycles Bearing Angle-Strained Alkynes

Angle‐strained alkyne‐containing π‐conjugated macrocycles are attractive compounds both in functional materials chemistry and biochemistry. Their interesting reactivity as well as photophysical and supramolecular properties have been revealed in the past three decades. This review highlights the recent advances in angle‐strained alkyne‐containing π‐conjugated macrocycles, especially their synthetic methods, the bond angles of alkynes (∠sp at C≡C−C), and their functions. The theoretical and experimental research on cyclo[n]carbons and para‐cyclophynes consisting of ethynylenes and para‐phenylenes are mainly summarized. Related macrocycles bearing other linkers, such as ortho‐phenylenes, meta‐phenylenes, heteroaromatics, biphenyls, extended aromatics, are also overviewed. Bond angles of strained alkynes in π‐conjugated macrocycles, which are generable, detectable, and isolable, are summarized at the end of this review

A cluster-based mean-field, perturbative and coupled-cluster theory description of strongly correlated systems

We introduce cluster-based mean-field, perturbation and coupled-cluster theories to describe the ground state of strongly-correlated spin systems. In cluster mean-field, the ground state wavefunction is written as a simple tensor product of optimized cluster states. The cluster-language and the mean-field nature of the ansatz allows for a straightforward improvement based on perturbation theory and coupled-cluster, to account for inter-cluster correlations. We present benchmark calculations on the 2D square $J_1-J_2$ Heisenberg model, using cluster mean-field, second-order perturbation theory and coupled-cluster. We also present an extrapolation scheme that allows us to compute thermodynamic limit energies very accurately. Our results indicate that, even with relatively small clusters, the correlated methods can provide an accurate description of the Heisenberg model in the regimes considered. Some ways to improve the results presented in this work are discussed

Exact Wave Packet Dynamics of Singlet Fission in Unsubstituted and Substituted Polyene Chains within Long-Range Interacting Models

Singlet fission (SF) is a potential pathway for significant enhancement of efficiency in organic solar cells (OSC). In this paper, we study singlet fission in a pair of polyene molecules in two different stacking arrangements employing exact many-body wave packet dynamics. In the non-interacting model, the SF yield is absent. The individual molecules are treated within Hubbard and Pariser-Parr-Pople (PPP) models and the interaction between them involves transfer terms, intersite electron repulsions and site-charge--bond-charge repulsion terms. Initial wave packet is constructed from excited singlet state of one molecule and ground state of the other. Time development of this wave packet under the influence of intermolecular interactions is followed within the Schr\"odinger picture by an efficient predictor-corrector scheme. In unsubstituted Hubbard and PPP chains, $2{}^1A$ excited singlet state leads to significant SF yield while the $1{}^1B$ state gives negligible fission yield. On substitution by donor-acceptor groups of moderate strength, the lowest excited state will have sufficient $2{}^1A$ character and hence results in significant SF yield. Because of rapid internal conversion, the nature of the lowest excited singlet will determine the SF contribution to OSC efficiency. Furthermore, we find the fission yield depends considerably on the stacking arrangement of the polyene molecules.Comment: 13 pages, 8 figures, 4 table

GENERATION, CHARACTERIZATION AND REACTIVITY OF COBALT DIAMOND CORE AND COBALT PEROXO COMPLEXES

The development of efficient and low-cost technologies that convert hydrocarbons, including methane, to liquid fuels through controlled functionalization of its inert C–H bond is a fundamental challenge. Also, the activation of carbon−hydrogen (C−H) bonds is the first step of functionalizing inert hydrocarbons. This transformation is a key step in many biological and synthetic processes. One representative example inspired by nature is the metalloenzyme called soluble methane monooxygenase (sMMO), a nonheme dinuclear iron-dependent enzyme that catalyzes the hydroxylation of the strong C–H bond of methane (bond dissociation energy BDE = 105 kcal/mol) using O2 as the oxidant. The catalytic cycle of sMMO has been extensively studied over decades, and features a highvalent bis-μ-oxo FeIV2(μ-O)2 “diamond core” intermediate called Q as the active oxidant for C–H bond activation. This research focuses on the study of an unprecedented highvalent CoIII,IV2(μ-O)2 complex supported by neutral tetradentate tris(2- pyridylmethyl)amine (TPA) ligand by one-electron oxidation of its CoIII2(μ-O)2 precursor. This new complex can activate C−H bonds 3−5 orders of magnitude faster than its iron and manganese counterparts, and represents the most reactive synthetic model for the sMMO enzymatic intermediate. This study expands the understanding of base metal complexes for C−H bond activation and serves as motivation to design C−H activation methods inspired by nature. Chapter 1 provides the introduction of C-H bond hydroxylation mechanism and the biological background that initially inspired this project. In Chapter 2, we reported the characterization of cobalt diamond core complexes supported by TPA and related ligands. In Chapter 3, we studied the reactivity of those complexes. In Chapter 4, we discovered that the open core species provides an excellent strategy to achieve substrate specificity and to be applied in the deaminative C(sp3)-N bond activation. Chapter 5 describes a proposed monomer [Co(III)(TPA)(O2)]+ species and its nucleophilic reactivity. Chapter 6 lays out the overall conclusions and points out a few future directions as the prospective scope of the entire project