Isomerism ethylene electronic

Ethylene electronic isomerism is introduced as a new concept and examined from the perspective of the generalized electronic diabatic (GED) scheme. In chemistry isomerism is related to distributions in space of atomic nucleus in one and the same adiabatic potential energy surface. Therefore, in this case cis and trans isomers would be indistinguishable when the four hydrogen atoms are identical. Nevertheless, in this paper we show that isomerism is an electronic... 

More detailed studies of the behavior of benzotriazoles upon electron impact provided evidence for the exclusive presence of the l//-benzotriazole tautomer in the gas phase. The A/t of 2//-benzotriazole is generated from 2-ethylbenzotriazole (66) by ethylene elimination isomerization to the l//-tautomer precedes the fragmentation <730MS(7)1267). 

The Nenitzescu process is presumed to involve an internal oxidation-reduction sequence. Since electron transfer processes, characterized by deep burgundy colored reaction mixtures, may be an important mechanistic aspect, the outcome should be sensitive to the reaction medium. Many solvents have been employed in the Nenitzescu reaction including acetone, methanol, ethanol, benzene, methylene chloride, chloroform, and ethylene chloride however, acetic acid and nitromethane are the most effective solvents for the process. The utility of acetic acid is likely the result of its ability to isomerize the olefinic intermediate (9) to the isomeric (10) capable of providing 5-hydroxyindole derivatives. The reaction of benzoquinone 4 with ethyl 3-aminocinnamate 35 illustrates this effect. ... 

Hartmann, M., A. Piippl et al. (1996). Ethylene dimerization and butene isomerization in nickel-containing MCM-41 and A1MCM-41 mesoporous molecular sieves An electron spin resonance and gas chromatography study. J. Phys. Chem. 100 9906-9910. 

In symmetric overcrowded or otherwise strained ethylenes, the strain may be partially released by rotation around the C=C bond or by other deformations, and the barrier to E-Z isomerization may be lowered compared to that of ethylene by ground state strain and by delocalization of the double-bond ir electrons into unsaturated substituents, forming a diradical transition state. The importance of the delocalization effect is illustrated by the low barrier (AC o = 23.2 kcal/ mol) in the diphenoquinone 125 (145), in which the ground state strain must be rather low. 

The presence of organolithium compounds in etheric solvents at temperatures above 0°C may lead to extensive decomposition of the solvent and solute a slow electron transfer side reaction of lithium naphthalene or sodium naphthalene with the THE solvent (equation 5) has been reported . The three isomeric forms of BuLi were shown to induce extensive decomposition of THE. The main path for this process is metallation at position 2 of THE, leading to ring opening and elimination of ethylene. An alternative path is proton abstraction at position 3, followed by ring opening. The presence of additives such as (—)-sparteine (24), DMPU (25), TMEDA and especially HMPA does not prevent decomposition but strongly affects the reaction path. ... 

Figure 7.7 (a) The potential energy of S0, Ti and Si states of ethylene and (b) its electronic configuration, as a function of twist angle during trans-cis isomerization. 

In the ethane-ethylene reaction in a flow system with short contact time, exclusive formation of n-butane takes place (longer exposure to the acid could result in isomerization). This indicates that a mechanism involving a trivalent butyl cation depicted in Eqs. (5.1)—(5.5) for conventional acid-catalyzed alkylations cannot be operative here. If a trivalent butyl cation were involved, the product would have included, if not exclusively, isobutane, since the 1- and 2-butyl cations would preferentially isomerize to the rm-butyl cation and thus yield isobutane [Eq. (5.9)]. It also follows that the mechanism cannot involve addition of ethyl cation to ethylene. Ethylene gives the ethyl cation on protonation, but because it is depleted in the excess superacid, no excess ethylene is available and the ethyl cation will consequently attack ethane via a pentacoordinated (three-center, two-electron) carbocation [Eq. (5.10)] ... 

Base-catalyzed rearrangement of ethylene oxides is a topic that baa, until now, received only limited attention in the literature, chiefly because epoxides undergo simple nudeophilio attack rather than isomerisation with most bases. Strictly speaking, a base-catalysed epoxide isomerization is one in which the initial event is direct proton abstraction from the oxide ring. This may bo followed by redistribution of bonding electrons in any of several possible ways, to give ultimately one or more carbonyl compounds. For the general case the course i>f such a reaction may be depicted a in Eq. (480),... 

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