Butadiene, electronic structure

Berry, R. S., J. Chew. Phys. 26, 1660, -electron structure of butadiene. Several methods including superposition of configurations. 

Among the recently published works, the one which showed that the cyclic structures of water clusters open up to form a linear structure above a certain threshold electric field value a was a systematic ab initio study on the effect of electric field on structure, energetics, and transition states of trimer, tetramer, and pentamer water clusters (both cyclic and acyclic) [36], Considering c/.v-butadiene as a model system, the strength and the direction of a static electric field has been used to examine the delocalization energy, the probabilities of some local electronic structures, the behavior of electron pairs, and the electronic fluctuations [37]. Another recent work performed by Rai et al. focused on the studies using the DFT and its time-dependent counterpart of effects of uniform static electric field on aromatic and aliphatic hydrocarbons [38],... 

For earlier ab initio calculations of the electronic structure of 1,3-butadiene see Refs.195 and 196). 

The electronic structure of 4 (and the other o-quinonoid heterocycles 1,2, and 3) has been discussed in the light of NMR data. For a series of hydrocarbons containing formally cisoid butadiene fragments (10 R and R not explicitly stated), the ratio of the vicinal coupling constants s.e)... 

In contrast to heterogeneous Ziegler-Natta catalysts, homogeneous catalysts based on biscyclopentadienyl derivatives of group 4 transition metals, which contain cationic metallocene species of formally d° 14-electronic structure, hardly promote the polymerisation of conjugated dienes, since the diene can act as a donor of four electrons rather than of two electrons as in monoolefin polymerisation (let us recall that the polymerisation of conjugated dienes is catalysed by half-sandwich metallocene-based catalysts). However, it has been reported [162] that statistical copolymers of ethylene and butadiene were obtained with the Cp2ZrCl2— [Al(Me)0]x catalyst. 

With this method, we clarified the electronic structures of the ground and excited states of benzene, butadiene, methane, and hydrogen molecules [1,2]. We also applied the method to valence excited states of polyenes [3] and then-cations [4]. In previous studies, we put our focus on the formalism of CASVB and its applicability to molecules in their equilibrium structures. 

For many simple compounds having no more than one double bond, the modern picture may be quite adequately represented by the Lewis structures (although the Lewis rules are noncommittal about the shapes of molecules). For compounds such as butadiene, benzene, and nitrous oxide, where there is extensive delocalization of electron density, the Lewis structures are not as suitable as the x-electron structures or, better still, as the streamer structures. Both of the latter type, however, are more difficult to draw and, for more complex molecules, more difficult to visualize they become extremely unwieldy when one attempts to use them to represent the progress of a chemical reaction. 

The DuPont ADN process involves hydrocyana-tion of butadiene (equations 5-8), catalyzed by air-and moisture-sensitive triarylphosphite-nickel(O) complexes [Ni(P(OAr)3)4]. The nickel is zero valent (see Oxidation Number) because it has its full complement of 10 electrons beyond the preceding inert gas (Ar) configuration, and the catalysts can actually be made directly from nickel metal and the phosphite ligands (see P-donor Ligands). The four phosphorus atoms each contribute an electron pair to give a total of 18 electrons, corresponding to the next inert gas (Kr), (see Effective Atomic Number Rule and Electronic Structure of Organometallic Compounds). 

Butadiene shows features common to all conjugated molecules, that is those in which the double bonds of classical chemistry cannot be uniquely allocated. According to the aufbau approach, its electronic structure, apart from that of the cr-bonded framework, would be The extra stabilisa-... 

As the chain length increases, the energy levels shown in Figure 7.17 for 1,3-butadiene increase in number and coalesce into bands. Thus, the conjugated electronic structure for the individual linear polymer molecule is described by bands, which previously we have seen only for extended three-dimensional solids (see Figs. 21.20 and 22.21). The ground state for the polymer chain is that of an insulator, with an energy gap between occupied and empty levels. 

Electrically conducting polymers combine the optical and electronic properties of inorganic semiconductors with the processing ease of conventional polymers. Their structures are continuations of the 1,3-butadiene structure to greater lengths, and the electronic structure for the individual molecule is described by bands. These polymers are made electrically conducting by doping. 

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