Ethylenic double bond

Historically, ethylene potymerization was carried out at high pressure (1000-3000 atm) and high temperature (100-250 °C) in the presence of a catalyst such as benzoyl peroxide, although other catalysts and reaction conditions are now more often used. The key step is the addition of a radical to the ethylene double bond, a reaction similar in many respects to what takes place in the addition of an electrophile. In writing the mechanism, recall that a curved half-arrow, or "fishhook" A, is used to show the movement of a single electron, as opposed to the full curved arrow used to show the movement of an electron pair in a polar reaction. 

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. 

Unsaturated organic molecules, such as ethylene, can be chemisorbed on transition metal surfaces in two ways, namely in -coordination or di-o coordination. As shown in Fig. 2.24, the n type of bonding of ethylene involves donation of electron density from the doubly occupied n orbital (which is o-symmetric with respect to the normal to the surface) to the metal ds-hybrid orbitals. Electron density is also backdonated from the px and dM metal orbitals into the lowest unoccupied molecular orbital (LUMO) of the ethylene molecule, which is the empty asymmetric 71 orbital. The corresponding overall interaction is relatively weak, thus the sp2 hybridization of the carbon atoms involved in the ethylene double bond is retained. 

Recently several examples of diolefin crystals in which the reaction behaviour deviates from the topochemical rule have been observed. For example, in the photoreaction of methyl a-cyano-4-[2-(4-pyridyl)-ethenyljcinnamate (2 OMe), the first reaction occurs exclusively at the pyridyl side although the distance between the ethylenic double bonds on the pyridyl side is exactly the same as that between the ethylenic double bonds on the ester side (4.049 A), as shown in Fig. 5 (Maekawa et al., 1991a). A few other unsymmetrical diolefin compounds display the same regioselective behaviour (Hatada, 1989). 

Methyl 4-[2-(ethylthiocarbonyl)ethenyl]cinnamate (3 SMe) crystallizes into a typical a-translation-type packing structure in which the distances between the ethylenic double bonds are 3.988 A and 4.067 A, respectively. However, the 3 SMe crystal is entirely photostable even though it should be photoreactive based on the topochemical rule (Sukegawa, 1991). Several examples of exceptionally photostable diolefin crystals have been found in compounds having a thioester moiety. Such anomalous behaviour of crystals such as 2 OMe and 3 SMe cannot be explained simply in terms of the topochemical rule since this rule involves only the positional relationship between the reactive olefin pair. 

In the crystal of 7 OEt, two molecules form a molecular pair as is the case in the crystal of 7 OMe. Considering the intermolecular distances between the ethylenic double bonds (3.714 and 3.833 A within the pair, and 4.734 and 4.797 A between the pairs), each molecule can react only with its partner in the molecular pair and not with any molecule of another pair. Since paired molecules are related by centrosymmetry, two pairs of facing ethylenic double bonds should be equal in photoreactivity, affording two... 

Here is a list of all dangerous reactions that are related to nitrile functional group behaviour. By active polymerisation is meant the polymerisation that affects the carbon-nitrogen triple bond. Polymerisations that are related to an ethylene double bond will be dealt with on p.336. So far as stability is concerned, it is difficult to say whether certain spontaneous reactions of certain nitriles are... 

The NFPA reactivity codes indicate the risks that are related to the propensity for polymerisation and/or instability of the nitrile group and of the potential ethylene double bond. The table below gives the available data with some contradictions between different sources, as usual (for acetonitrile, code 1 seems to make more sense)... 

Alder-Ene Reactions. An ene-iminium one-pot cyclization proceeds smoothly in a mixture of water-THF (Eq. 12.66). 138 The reactivity of the ene-iminium substrates is highly dependent on the substitution pattern of the ethylenic double bond. This methodology can be used to form homochiral pipecolic acid derivatives. 

Polymers are formed via two general mechanisms, namely chain or step polymerisation, originally called addition and condensation, respectively, although some polymerisations can yield polymers by both routes (see Chapter 2). For example, ring opening of cyclic compounds (e.g., cyclic lactides and lactams, cyclic siloxanes) yield polymers either with added catalyst (chain) or by hydrolysis followed by condensation (step). Many polymers are made via vinyl polymerisation, e.g., PE, PP, PVC, poly(methyl methacrylate) (PMMA). It could be argued that the ethylenic double bond is a strained cyclic system. 

A liquid produced by the addition of chlorine to the ethylene double bond. It is reacted with sodium polysulphide to produce polysulphide polymers, trade name Thiokol. 

Later, Patterson and Hibbert (S3) stated that ultraviolet absorption of lignin corresponded with the absorptions of hydroxy derivatives of 4-(4,hydroxy-3,methoxyphenyl)-l-propanone and l-(4,hydroxy-3, 5,dimethoxyphenyl)-4-propanone. These authors, therefore, assumed the presence in lignin of a carbonyl group, or of an ethylenic double bond conjugated with an aromatic nucleus. They ascribed the 280 mp band to m-position freedom in the benzene ring and the 310 mp baud to a masked carbonyl group in conjugation with a benzene nucleus. 

This compound chemiluminesces when exposed to air or oxygen. Its CL was first demonstrated by Fletcher and Heller [47, 48] and suggested to occur via formation of a dioxetane by addition of oxygen across the ethylenic double bond. Cleavage of the dioxetane to form excited tetramethylurea results in excitation of the tetrakis (dimethylamino) ethylene, whose CL is in good agreement with the fluorescence spectrum of the parent compound. The reaction has been used for the analysis of oxygen [49, 50],... 

A particularly dramatic effect of hyperconjugation on the form of the ethylenic double bond NBOs is shown in Fig. 3.50. This figure depicts one of the two equivalent C=C bond and antibond NBOs of vinylamine, twisted slightly out of coplanarity with the nitrogen lone pair with dihedral

[Pg.219]

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 chlorodifluoromethylated ketone 130 proved to be a valuable substrate for promoting SrnI subtitution reaction with sodium phenylthiolate and to generate a new a-(phenylthio)-a,a-difluoroacetophenone derivative 131 (Equation 57) <2001TL3459>. Upon treatment with nitronate anions under classical SrnI reaction conditions or MW irradiation, 6-chloromethyl-5-nitro-imidazo[2,l- ]thiazole 132 yielded 5-nitroimidazothiazoles bearing a trisubstituted ethylenic double bond at the 6-position (Equation 58) <2001SC1257>. 

At the beginning of the polymerization reaction, the viscosity of the medium is low, and efficient rotation (about the ethylenic double bond and the single bond linking ethylene to the phenyl ring) accounts for the low fluorescence quantum yield. After a lag period, when approaching the polymer glassy state, the fluorescence intensity increases rapidly as a result of the sharp increase in... 

In order to determine if the diminish of ethylenic double bond of the polymer by the attack of nitrene occurs, the ratio of IR absorbances due to v(C=C) of ethylenic double bond(3100cm-1) and due to v(CH) of alkane(2990cm-l) has been determined for the unirradiated film, irradiated film, benzene extract and Soxhlet extract(Table 3). 

Mechanism [ill] represents crosslinking due to aziridine ring formation. This mechanism is supported by the decrease of ethylenic double bond of 1,2-polybutadiene and the fact that a large amount of aziridine compound is formed in the reaction of phenyl-nitrene with unsaturated olefine monomers, although the direct observation of it in 1,2-polybutadiene film matrix has not been accomplished in the present study. 

The prototype of the present surface photografting is the surface photoreaction of maleic anhydride(MAH) onto poly(butadiene) film(15). Although fair improvement of surface wettability was achieved, photoaddition of MAH cannot be applied to other polymers having no ethylenic double bonds. The present process is applicable to almost all polymers except for poly(tetrafluoroethy-lene) and its analogues. 

It is clear that some information is lost as a result of our approximation, specifically regarding the individual bonds formed by sp carbon atoms, but the total of the F values in a molecule is expected to be generally reasonably accurate. The salient feature of ethylenic double bonds, namely, the inward displacement of tt orbital centroids on the C=C axis revealed by direct calculations, and its important role in energy calculations, can now be put in a clear perspective and efficiently tested for large collections of molecules. 

Figure 4.20 Variation of potential energy function for ground and excited states of biphenyl (single bond) and ethylene (double bond).

Compounds with an isolated ethylenic double bond lead to a strong absorption band around 170nm, where the position of this band depends on the presence of heteroatom substituents. For example, ethylene Amax = 165nm (e = 16000). 

In Figure 3A, in contrast to Figure 3B, some portion of the "main peak" would be ascribed to band I of deprotonated form of XI. Nevertheless, this would not affect at all the former discussion — the swift formation of ethylenic double bond that is conjugated with an adjacent double bond. This deduction is clearly confirmed by Figure 3A "main peak continues to increase sharply even after the "side peak" begins to decrease. 

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