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Molecular Orbital Theory of Surfaces
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
As the list of topics for this handbook shows, there are many probes of surfaces, and some give surface visualization data relatively directly, as do the tunneling electron and field emission microscopes. Others, such as ellipsometry and electron spin resonance spectroscopy, are indirect, meaning additional data from other probes are needed to create a reasonable, unique surface structure hypothesis. Some, like high-resolution electron energy loss and surface enhanced Raman vibrational analysis, are in between; data from such measurements are sometimes sufficient for proposing surface structures with confidence, if not absolute certainty, because of known bond frequency-bond order-structure relationships. Theoretical models and calculations are used to interpret the data and corroborate the conclusions of measurements using each of the surface probe techniques. This chapter deals with the use of molecular orbital theory in this context.
Macromolecular Architecture and Molecular Modelling of Dendrimers
Published in Neelesh Kumar Mehra, Keerti Jain, Dendrimers in Nanomedicine, 2021
Rahul Gauro, Keerti Jain, Vineet Kumar Jain, Neelesh Kumar Mehra, Harvinder Popli
Molecular orbital theory/linear arrangement of atomic orbits and orbitals (electrons) specifically treated in quantum mechanics. Quantum mechanics is speculated to be more precise results in fundamental constants and related quantities determination (Ramachandran et al. 2008).
Conjugation and Reactions of Conjugated Compounds
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
The m and n refer to the number of π-electrons that are transferred during the reaction. Typical examples of [m+n] reactions are [2+2], [4+2], etc. The Diels–Alder reaction is an example of a [4+2] pericyclic reaction. A [2+2] reaction is one where a 2π system reacts with another 2π system. A [4+2] systems is one where a 4π system reacts with a 2π system, and so on. What is frontier molecular orbital theory?
A family of methoxide-bridged Cu(II) compounds with N-heterocyclic ligands: dimers and chains
Published in Journal of Coordination Chemistry, 2023
Alma P. Araujo-Martinez, Kesli Faber, Nathan Huynh, Diane A. Dickie, Christopher P. Landee, Mark M. Turnbull, Brendan Twamley, Jan L. Wikaira
Magnetostructural relationships in transition metal complexes have been a topic of interest for decades. Cu(II) complexes have been studied extensively in this field, as they can behave as low-dimensional magnets, in which the magnetic exchange occurs in one or two dimensions, such as chains, ladders and layers [1]. There is special interest in bridged compounds, which can be tuned to have different magnetic properties by adjusting the bridging structure. Series of hydroxy-bridged Cu(II) dimeric complexes with different ancillary ligands have been studied for their magneto-structural relationships. Hatfield, Hodgson and co-workers determined that the magnetic exchange in these bridged complexes depends on the Cu-O-Cu bridging angle [2]. The bridging angle and the singlet-triplet splitting (J) of four Cu(II) dimeric complexes with double hydroxy-bridges were examined, and the parameters followed a linear relationship [2]. Complexes with bridging angles above 97.6° were antiferromagnetic, and those with angles below 97.6° were ferromagnetic [3]. The correlation between these parameters was explained through molecular-orbital theory. The molecular orbitals involved in the Cu-O-Cu-O ring that forms in the dimer exhibit a triplet ground state when the bridging angle is 90° due to orthogonality of the orbitals, making the compound ferromagnetic [3]. As the angle increases, the orbital overlap breaks the degeneracy and creates a singlet ground state, making the compound antiferromagnetic [3].
Complexation and enantioselectivity of novel bridge-like uranyl- 2-((1Z,9Z)-9-(2-Hydroxyphenyl)-3,5,6,8-tetrahydrobenzo[h][1,4,7,10] dioxadiazacyclododecin-2-yl)-5-methoxyphenol with chiral organophosphorus pesticide enantiomers of R/S-malathions
Published in Environmental Technology, 2022
Xuebing Tao, Rong Yang, Yang Xiao, Lifu Liao, Xilin Xiao, Changming Nie
In frontier molecular orbital theory [41,42,44–46], HOMO represents the highest occupied molecular orbital, and LUMO represents the lowest unoccupied molecular orbital. Therefore, the energy of HOMO determines the ability of a molecule to provide electrons [47,48], and the energy of LUMO determines the ability of a molecule to accept electrons [49–51]. △EL-H is the energy gap between LUMO and HOMO of the compound which reflects the energy of the transition required for a molecule goes from the ground state to the excited state [52–54]. Table 3 lists the frontier orbital parameters of the six receptor-guest complexes, among which EHOMO and ELUMO were calculated directly, and the energy gap (△EL-H), chemical hardness (η), chemical potential (Φ), electronegativity (χ) and electrophilicity index (ω) of the six receptor-guest complexes were obtained by the following formulas [55,56].
Excited-state intramolecular double proton transfer mechanism associated with solvent polarity for 9,9-dimethyl-3,6-dihydroxy-2,7-bis(4,5-dihydro-4,4-dimethyl-2-oxazolyl)fluorene compound
Published in Molecular Physics, 2022
Liying Song, Xuan Meng, Jinfeng Zhao, Haiyun Han, Daoyuan Zheng
For the sake of understanding the background of the computational results, we briefly introduce the computational methods used in this paper. All the theoretical simulations in this paper were performed using Gaussian16 software, employing DFT and TDDFT theoretical methods in association with the B3LYP and the 6-311+G(d) level basis set [41]. After comprehensive consideration, we choose the integral equation formalism variant of the polarisable continuum model (IEF-PCM) as the solventisation model, which has the ability to compensate for the charge escape from the cavity [40,57,58]. It is possible to reduce the computational burden of simulating solvent molecules and specific interactions with solutes. Under this solvent model, we picked cyclohexane, chloroform and acetonitrile (i.e. along with the solvent polarity from low to high) as solvents to explore the effect of solvent polarity on the ESIPT behaviour of (Oxa-OH)2 system [55]. The reduced density gradient (RDG) model, topological analysis, calculated hydrogen bonding energy, and infrared vibrational spectra without imaginary frequencies were used to explore the changes in excited-state hydrogen bonding. The frontier molecular orbital theory was used to examine the excited-state electron transfer. The potential energy surfaces were also constructed to investigate the mechanism of excited-state proton transfer.