Bonds ethylene

Union Carbide abandoned the ketene—crotonaldehyde route in 1953 in favor of the oxidation of 2,4-hexadienal made by acetaldehyde condensation. A silver compound used as the catalyst prevented peroxidation of the ethylenic bonds (39,40). Thein plant operated until 1970. 

Ethylene, bond angles in, 16 bond lengths in, 16 bond strengths in, 16 electrostatic potential map of, 74, 147... 

Assuming confirmation by further work, these compounds are the first Pu compounds to show Pu-ethylenic bonding. The nature of this bonding is unknown, but participation of 5f orbitals with it orbitals of the ethylene double bond, though unlikely, should be considered. The large and easily polarizable iodide ions could be the key factor in stabilizing the proposed Pu+3-ethylene bonds. 

Systematic studies of the selectivity of electrophilic bromine addition to ethylenic bonds are almost inexistent whereas the selectivity of electrophilic bromination of aromatic compounds has been extensively investigated (ref. 1). This surprising difference arises probably from particular features of their reaction mechanisms. Aromatic substitution exhibits only regioselectivity, which is determined by the bromine attack itself, i.e. the selectivity- and rate-determining steps are identical. 

While conformation II (Fig. 2.34) of Uke-y -amino acids is found in the 2.614-helical structure, conformation I, which similarly does not suffer from sy -pen-tane interaction, should be an appropriate alternative for the construction of sheet-like structures. However, sheet-like arrangement have not been reported so far for y-peptides composed of acyclic y " -amino acid residues. Nevertheless, other conformational biases (such as a,/9-unsaturation, cyclization between C(a) and C(y)) have been introduced into the y-amino acid backbone to restrict rotation around ethylene bonds and to promote extended conformation with formation of sheets in model peptides. Examples of such short chain y-peptides forming antiparallel (e.g. 152 [208]) and parallel (e.g. 153-155 [205, 208]) sheet-hke structures are shown in Fig. 2.38. 

Thus, whether the remaining ethylenic bond of a given unit is incorporated within the chain (V) or in a pendant vinyl group (VI) external to the chain is governed by the manner of addition of the succeeding unit. The 1,4 unit may occur as either the cis or the trans isomer, i.e. 

Fig. 7.9. The possible mode of orbital overlapping of tungsten d orbitals with two ethylenic bonds...

Intermolecular PKRs proceed especially easily with strained alkenes, e.g., nor-bornene, norbomadiene, and cyclobutene [97]. Nevertheless, highly strained MCP gave unsatisfactory results when reacted at 20 °C in hexane with acetylene, propyne, or phenylacetylene, both in terms of yields (10-15%) and of regioselec-tivity of the attack to the ethylenic bond (ca. 1 1) [100a, 103]. The reagents were consumed, but extensive tar formed and no variation in reaction conditions was successful. 

In contrast, polar and resonance effects must be separated in order to analyze the data for a-substituted arylolefins [ArC(R)=CHR with R H]. Their bromination involves open carbocation intermediates only. Resonance effects cannot be fully developed at the transition states, since the aromatic ring is not in the same plane as that of the developing carbocation, because of steric constraints. Accordingly, application of (33) gives pT < pn. Attenuation of resonance arises mainly from stereochemical factors, at least in the monosubstituted 1,1-diphenylethylene [20] and a-methylstilbene [21] series the pr/pn ratios can be related to the dihedral angle between the substituted phenyl ring and the plane of the ethylenic bond. 

The two violet forms are both solvated. X-Ray structure analysis showed that the unsolvated yellow crystal adopts a doubly folded geometry while the violet cubes adopt a twisted conformation. Both structures owe their deformations to repulsive short N- N contacts. The central ethylene bond in the yellow conformer is completely planar (136.2 pm) while in the violet cube conformer the same bond is twisted 48.1° and much longer (138.8 pm). 

As shown in (5.84b), the characteristic feature of the Diels-Alder reaction is the addition of an ethylenic double bond (dienophile) across the 1,4-positions of a conjugated diene to give a cyclohexene ring product. The ethylenic bond is usually... 

The electron impact mass spectra of 3-methyl-4-nitro-5-styryl-isoxazoles exhibit, on the contrary, only negligible loss of OH"80. This has been interpreted in terms of an isoxazole-to-azirine rearrangement80. The latter fragments directly to an abundant cinnamoyl ion as well as rearranges to oxazole and an epoxide through an intramolecular oxidation of the ethylenic bond by the nitro group80 see Scheme 10. 

OM-DM reaction of ewdo-tricyclo[5.2.2.02,6]undeca-3,8-diene (194) was found166 to proceed with high regio- and stereoselectivity, giving mainly 4-ew-hydroxy-encfo-tricyclo [5.2.2.02,6]undec-8-ene (195) together with 196 (equation 164). Saturation of the 8,9-ethylenic bond in 194 resulted in a large reduction in reactivity as well as in stereoselectivity. 

These results have been interpreted in terms of trans addition of mercuric ion and nucleophile where the attack of the mercuric ion takes place from the more hindered side of the diene molecule. A transition state 197, involving an endo attack of mercuric ion with some stabilization by coordination to the 8,9-ethylenic bond to the mercury atom, has been proposed to support the suggested mechanism. Analogously, and in sharp contrast to the results obtained167 in the mercuration of norbomadiene which reacts with mercury salts via the usual scheme of exo-syn addition, the principal pathway in the mercuration of bicyclo[2.2.2]octa-2,5-diene is the formation of endo-syn products (equation 165). 

Ratera et al. (2003) discovered valence tautomerism in the ferrocene connected through the ethylenic bond with perchlorotriphenylmethyl radical. As ascertained by Moessbauer spectroscopy, this species in the solid state exhibited a thermally induced intramolecular electron transfer resulting in the formation of ferrocenium and perchlorotriphenylmethyl anion moieties. The authors used the initial species in its trans form. If the cis form would be available, the possibility of rotation around the ethylenic bond would be interesting to disclose. According to the authors, the interconversion of the cation-radical and anion centers proceeds gradually. At ambient temperature, equilibrium composition of the tautomers is achieved. This peculiarity is important with respect to potential technical applications. 

It would also be interesting to check the ability of the ruthenocene acrylonitrile cation-radical to rotate around the ethylene bond Ruthenocenyl is weaker than ferrocenyl as a donor substituent (Laus et al. 2005). The particular property of rotating around the ethylenic bond in cation-radicals is a method of elucidating an electronic structure. 

On these same conditions, the reaction of 1,1-2,2-isomer is reversible (Scheme 2.26). With respect to the ethylene bond plane, the phenyl rings deviate only 30° in the 1,2-1,2-isomer and 90° in 1,1-2,2-isomer (Wallwork 1961, Todres and Bespalov 1972). 

In summary, the copper ion transfers an electron from the unsaturated substrate to the diazo-nium cation, and the newly formed diazonium radical quickly loses nitrogen. The aryl radical formed attacks the ethylenic bond within the active complexes that originated from aryldiazo-nium tetrachlorocuprate(II)-olefin or initial arydiazonium salt-catalyst-olefln associates and yields >C(Ar)-C < radical. The latter was detected by the spin-trap ESR spectroscopy. The formation of both the cation-radical [>C=C<] and radical >C(Ar)-C < as intermediates indicates that the reaction involves two catalytic cycles. In the other case, radical >C(Ar)-C < will not be formed, being consumed in the following reaction ... 

Compounds containing n systems have an affinity to the metallic surface and are arranged on the surface in a parallel manner. The ethylene bond of a-methyl-p-isopropyl stilbene is responsible for adsorption, and the substituents deviate from the metal surface. It is well known that alkali... 

The hydrogenation of carbonyl groups in compounds containing ethylenic bonds to obtain the corresponding unsaturated alcohols is a very important reaction in the fine chemicals field. Extensive work has been carried out to develop heterogeneous catalysts for these reachons, copper chromite being one of the first systems studied [69, 70]. Transihon metals are widely used catalysts for these reachons. 

In enediones in which two carbonyl groups of a diketone are linked by an ethylenic bond tin [174] and chromous chloride [196] reduce only the double bond, and none of the conjugated carbonyl groups. A double bond conjugated with one carbonyl group only is not reduced. Refluxing cholest-4-ene-3,6-dione with chromous chloride in tetrahydrofuran yielded 49% of 5/S-cholestane-3,6-dione, and a similar reduction of cholesta-l,4-diene-3,6-one gave 5)S-cholest-l-ene-3,6-dione [196]. 

The vibrational spectrum of LiC2H4 presents some striking similarities to that of ethylene bonded to other metals . The C—C stretching and in-phase CH2 scissoring modes were found to be very strongly IR-activated. The other symmetrical vibrations, CH2 wagging and Li—C stretching motions, were detected at about 700 and 300 cm 48,50 ... 

All factors that influence the stability of the transition metal-carbon bond (Mt-R) and/or the stability of the transition metal-ethylene bond (M-pethylene) are liable to affect the course of the reaction. Such factors are ... 

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