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Conducting Polymers
Published in Ram K. Gupta, Conducting Polymers, 2022
Suba Lakshmi Madaswamy, N. Veni Keertheeswari, Ragupathy Dhanusuraman
The band theory can be supported by using molecular orbital theory. Two new molecular orbitals can be formed by combining one p orbital from one carbon atom and another p orbital from another carbon atom. The bonding molecular orbital has lower energy than the other orbitals. The orbital with the highest energy is known as the anti-bonding molecular orbital (ABMO). Two electrons from two carbon atoms fill the bonding molecular orbital because electrons in this orbital are more stable. A pi bond is formed by these two electrons sharing the same orbital. The bonding molecular orbital has the highest occupied molecular orbital (HOMO) in this case, while the ABMO has the lowest unoccupied molecular orbital (LUMO). The bandgap energy, or the energy required for electron activation, is the difference in energy between HOMO and LUMO. An unlimited number of p orbitals exist in CPs with an indefinitely long polymer chain, and the innumerable molecular orbitals eventually form a band between the conduction and valence bands. Electrons may move from one band to another with less activation energy as the bandgap comes closer, and the polymer finally becomes metallic [9].
Materials for Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
First, let us briefly review molecular orbital concepts and theory. Molecular orbitals (MOs) are the solutions of the Schrӧdinger’s equation for molecules in the same way as atomic orbitals are solutions of this equation for atoms. Two atomic orbitals overlap to give two MOs: the molecular orbital at a lower energy than the overlapping atomic orbitals is called a bonding molecular orbital, whereas the molecular orbital at a higher energy than the overlapping orbitals is known as an antibonding molecular orbital.
A DFT study on selective adsorption of NH3 from ammonia synthesis tail gas with typical aliphatic boranes
Published in Molecular Physics, 2023
Qingyu Zhang, Jin Mao, Wencai Peng, Han Li, Liqiang Qian, Wanxi Yang, Jichang Liu
Figure 1 also presents the HOMO and LUMO orbital shapes of NH3, N2, H2 and CH4, and Table 2 lists the corresponding orbital energies as well as Mulliken charges, dipole moments (μ) and polarizabilities (α) of adsorbates. According to the orbital shape in Figure 1, the HOMO orbital of NH3 is composed with in phase combination of N 2p atom orbital collinear with principal rotation axis and three H 1s atom orbitals, and is mainly contributed by the lone pair electrons of N atom. The LUMO orbital of NH3 is composed with out of phase combination of N 2s atom orbital and three H 1s atom orbitals, and can be regarded as three σ-antibonding orbitals of N and H. The HOMO of N2 is a bonding σ-molecular orbital composed of two N 2p atom orbitals approaching ‘head-to-head’, and the LUMO is a π anti-bonding molecular orbital composed of two N 2p atoms approaching ‘shoulder by shoulder’. The HOMO orbital of H2 is a σ-bonding molecular orbital composed of the in phase combination of two 1s orbitals of two H atoms, and LUMO is a σ-antibonding molecular orbital composed by the out of phase combination of two 1s orbitals of two H atoms. The HOMO of CH4 is provided by the in phase combination of C 2p atom orbital and four H 1s atom orbitals, and the LUMO is an anti-bonding orbital composed of C 2s atom orbital and four H 1s atom orbitals.
Understanding oxidative addition in organometallics: a closer look
Published in Journal of Coordination Chemistry, 2022
Nabakrushna Behera, Sipun Sethi
Oxidative addition, in general, occurs both as inter- and intramolecular processes. In both cases, the oxidative products are obtained by shifting of non-bonding d-electron density from the metal to X–Y, a consequence of metal-to-ligand charge transfer (MLCT); a pair of electrons is involved in this process. These electrons populate the anti-bonding molecular orbital (σ*) of the corresponding X–Y bond which subsequently transforms into two anionic ligands as Xˉ and Yˉ owing to zero bond order (B.O.). If both of the ligands remain in the coordination sphere after the reductive cleavage of X–Y, then one may expect the occurrence of oxidative addition. Scheme 2 with its simplified molecular orbital (MO) diagram illustrates X–Y bond breaking qualitatively due to charge transfer. The oxidative addition which is normally considered to be more classical as in the case of type ‘A’ can be explained by this model. Very often, substrates providing a lower energy σ* orbital than d-orbital are prone to oxidative addition irreversibly. It will be reversible if the energy of the σ* orbital is more than the d-orbital. For instance, the σ* orbital of H2 rather occurs at higher energy than d-orbital for which the exchangeability between hydrogen molecule and the corresponding dihydride complexes is established easily.
4,5,9,10-Tetrahydrocycloocta[1,2-c; 5,8-c′]dithiophene from bis(2-chloropropen-3-yl)sulfide: spectral and theoretical monitoring of the formation
Published in Journal of Sulfur Chemistry, 2021
Vladimir I. Smirnov, Lidiya M. Sinegovskaya, Vladimir A. Shagun, Valentina S. Nikonova, Nikolai A. Korchevin, Igor B. Rozentsveig
The UV spectrum of the starting compound 2 shows an absorption band with a shoulder at 226 nm (lg ϵ 3.20) (Figure 1(b)) due to the π→π*-transition of electron from the occupied bonding molecular orbital to the free anti-bonding π*-orbital in the chlorpropenyl group [14]. In the spectrum of the target product 1, a band with an absorption maximum at 242 (lg ϵ 3.81) and a shoulder at 281 nm (lg ϵ 3.0) are observed (Figure 1(b)).