Intermediate ethylenic bond

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. 

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 ... 

In the reaction of hydrazine with 2-(l-alkoxyalkylidene)-l,3-dicarbonyl compounds, the 13 C NMR spectral evidence indicates that the only point of initial hydrazine attack is the carbon atom in die ethylene bond and the only observed intermediate is the corresponding enehydrazine. MNDO calculations of the electronic characteristics showed that the reaction obeys orbital control.75... 

The mechanisms of the reaction involving oc,(3-unsaturated ketones and hydrazines were studied in several publications [30, 66, 67, 68, 69, 70, 71, 72, 73, 74]. The first stage of the reaction is the addition of hydrazine to the carbonyl group of the ketone (compound 61, Scheme 2.15). Subsequent cycliza-tion by addition of the second nucleophilic center to the ethylene bond under acidic conditions is the rate-determining stage—its rate significantly depends on the stereochemistry and electronic structure of the intermediate hydrazone 62 (Scheme 2.15). 

Silver is an important metallic catalyst for the selective oxidation of ethylene. The silver catalyst is used to selectively convert ethylene to ethylene epoxide, an important intermediate for antifreeze. Whereas the epoxidation of ethylene proceeds with high selectivity on oxidic silver phases, metallic silver surfaces give only total oxidation of ethylene. Electron-deficient O is created on oxidized silver surfaces and this readily inserts into the electron-rich ethylene bond. 

Isotopic examinations indicate that the products obtained from traws-divinyloxirane are formed from a common ylide intermediate. " Further work on the thermal behavior of cis- and traws-vinylaryloxiranes has revealed that the stereoselectivity of the reactions depends primarily on the configuration of the ethylene bond (Eq. 386). " ... 

Introduction of a triple bond into a pre-existing carbon skeleton is almost always effected by a method that starts from compounds containing an ethylenic bond or proceeds through such compounds as intermediates.177 The reaction most commonly used is dehydrohalogenation of appropriate halogen compounds, namely, either of chloro- or bromo-alkenes (1 or 2) or of dichloro-or dibromo-alkenes (3, 4, or 5) carrying the two halogen atoms on vicinal or the-same carbon atom. 

The photochemical addition of 9,10-phenanthraquinone, tetrachloro-1,2-benzoquinone (and benzil) to alkenynes (285) has been reported.167 The addition of the quinones takes place to the ethylenic bond of the alkenyne to yield alkynyl dioxins (286) and (287). The reaction is not stereospecific and a biradical intermediate is proposed to account for the loss of the stereochemical integrity of the olefin. Ishibe et a/.168 have published the results of an investigation of the photoaddition of p-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-benzoquinone,... 

Attempts to synthesize perchloropropenylbenzenes, such as a,p-dichloro-propenylbenzene, with reagent BMC had been unsuccessful (Ballester and Riera, 1960). An alternative way was devised, consisting in the condensation of perchlorotoluene with trichloroethylene in methylene chloride by means of aluminium chloride. Such a process had to surmount significant steric hindrance, particularly the formation of a sterically strained intermediate adduct, and therefore the reaction had to be conducted at moderate temperature. It was nevertheless expected that steric strain would assist the subsequent hydrogen chloride elimination to form the ethylene bond (72). 

It is essential to apply both tests, since some symmetrically substituted ethylenic compounds (e.g., ilbene C4H5CH=CHCjHj) react slowly under tbe conditions of the bromine test. With dilute permanganate solution the double bond is readily attacked, probably through the intermediate formation of a cis diol ... 

Section 14 15 Coordination polymerization of ethylene and propene has the biggest eco nomic impact of any organic chemical process Ziegler-Natta polymer ization IS carried out using catalysts derived from transition metals such as titanium and zirconium tt Bonded and ct bonded organometallic com pounds are intermediates m coordination polymerization... 

Chlorine reacts with saturated hydrocarbons either by substitution or by addition to form chlorinated hydrocarbons and HCl. Thus methanol or methane is chlorinated to produce CH Cl, which can be further chlorinated to form methylene chloride, chloroform, and carbon tetrachloride. Reaction of CI2 with unsaturated hydrocarbons results in the destmction of the double or triple bond. This is a very important reaction during the production of ethylene dichloride, which is an intermediate in the manufacture of vinyl chloride ... 

The mechanism of the cobalt-cataly2ed oxo reaction has been studied extensively. The formation of a new C—C bond by the hydroformylation reaction proceeds through an organometaUic intermediate formed from cobalt hydrocarbonyl which is regenerated in the aldehyde-forrning stage. The mechanism (5,6) for the formation of propionaldehyde [123-38-6] from ethylene is illustrated in Figure 1. 

Structure. The straiued configuration of ethylene oxide has been a subject for bonding and molecular orbital studies. Valence bond and early molecular orbital studies have been reviewed (28). Intermediate neglect of differential overlap (INDO) and localized molecular orbital (LMO) calculations have also been performed (29—31). The LMO bond density maps show that the bond density is strongly polarized toward the oxygen atom (30). Maximum bond density hes outside of the CCO triangle, as suggested by the bent bonds of valence—bond theory (32). The H-nmr spectmm of ethylene oxide is consistent with these calculations (33). 

The double bond migration which normally occurs on forming ethylene ketals from A -3-ketones has frequently been utilized to form derivatives of the A -system. The related transformation of A -3-ketones into A -3-alcohols is usually accomplished by treatment of the enol acetate (171) (X = OAc) with borohydride. This sequence apparently depends on reduction of the intermediate (172) taking place faster than conjugation ... 

The above cycloaddition process consists of two separate [3-1-2] cycloaddition steps and represents a 1,3-2,4 addition of a multiple bond system to a hetero-1,3-diene [7S7]. The structure ot the azomethine imine intermediate has been proved unequivocally by X-ray analysis [195] Ethylene [194], acetylene [/iS2] . many alkyl- and aryl- as well sgemmal dialkyl- and diaryl-substituted alkenes [196,197, 198, 199], dienes [200], and alkynes [182, 201], certain cyclic alkenes [198, 199,... 

We call the carbocation, which exists only transiently during the course of the multistep reaction, a reaction intermediate. As soon as the intermediate is formed in the first step by reaction of ethylene with H+, it reacts further with Br in a second step to give the final product, bromoethane. This second step has its own activation energy (AG ), its own transition state, and its own energy change (AG°). We can picture the second transition state as an activated complex between the electrophilic carbocation intermediate and the nucleophilic bromide anion, in which Br- donates a pair of electrons to the positively charged carbon atom as the new C-Br bond starts to form. 

Ethylene oxide, the simplest epoxide, is an intermediate in the manufacture of both ethylene glycol, used for automobile antifreeze, and polyester polymers. More than 4 million tons of ethylene oxide is produced each year in the United States by air oxidation of ethylene over a silver oxide catalyst at 300 °C. This process is not useful for other epoxides, however, and is of little value in the laboratory. Note that the name ethylene oxide is not a systematic one because the -ene ending implies the presence of a double bond in the molecule. The name is frequently used, however, because ethylene oxide is derived pom ethylene by addition of an oxygen atom. Other simple epoxides are named similarly. The systematic name for ethylene oxide is 1,2-epoxyethane. 

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