Olefins electronic spectra

SbCla is a relatively weak Lewis acid, since in the presence of a mixture of mesity-lene and benzoyl chloride it gives a complex with mesitylene Antimony penta-chloride is stronger and gives a 1 1 complex with perylene whose electronic spectrum is similar to that of the perylene cation Complexation has been claimed between antimony pentafluoride and aromatic olefins such as 1,1-diphenylethylene and stilbene ... 

In this category appear all the alkenes having at least one (3(C-C) bond. The occurrence of the primary (3(C-C) bond rupture in acyclic olefins was first shown to be the main process by Callear and Lee. Using a flash photolytic system ( > 160 nm), they generated various allylic radicals and were thus able to measure the electronic spectrum of these radicals in the 210-250 nm region (61). The quantum yields of the rupture of this bond is 0.8 (47,49,62). For example, the 147.0 and 163.3 nm photolysis of n-l-hexene leads to the primary (3(C-C) bond rupture with a high quantum value (63) ... 

The simplest examples of this type of compound are enamines derived from the quinuclidine skeleton (67). The formulation of enamines of qflmuclidine in a inesomeric form would violate Bredt s rule. Actually, the ultraviolet spectrum of 2,3-benzoquinuclidine shows that there exists no interaction of aromatic ring tt electrons and the nitrogen-free electron pair (160,169). The overlap of the olefinic tt orbital and the lone pair orbital on nitrogen is precluded. 

The choice of the desired CM-partner directly influences the choice of the catalyst [147], Comparing the GII and the HII catalysts shows that the latter has access to a much broader spectrum of cross-partners [148], It is possible to use electron deficient cross-partners like acroleine, perfluorinated olefins, acrylonitrile, or other o / -unsaturated carbonyls, whereas GII leads to no reaction or very low conversions due to side-reactions in these cases. 

The order of reactivity of these three catalysts towards alkenes (but also towards oxygen) is 1 > 3 > 2. As illustrated by the examples in Table 3.18, these catalysts tolerate a broad spectrum of functional groups. Highly substituted and donor- or acceptor-substituted olefins can also be suitable substrates for RCM. It is indeed surprising that acceptor-substituted alkenes can be metathesized. As discussed in Section 3.2.2.3 such electron-poor alkenes can also be cyclopropanated by nucleophilic carbene complexes [34,678] or even quench metathesis reactions [34]. This seems, however, not to be true for catalysts 1 or 2. 

Thiete 2 shows a doublet (IH) at S 6.50, a multiplet (IH) at 3 5.60, and a doublet (2H) at 8 3.80. In the spectrum of thiete 1,1-dioxide, the signal of the j -olefinic proton is at lower field than that of the a-olefinic proton. The P atom has a lower electron density than the a atom, because of the polarization of electrons in the ring by the sulfone group. 

As a result of the recognized role of transition metal hydrides as l reactive intermediates or catalysts in a broad spectrum of chemical reactions such as hydroformylation, olefin isomerization, and hydrogenation, transition metal hydride chemistry has developed rapidly in the past decade (J). Despite the increased interest in this area, detailed structural information about the nature of hydrogen bonding to transition metals has been rather limited. This paucity of information primarily arises since, until recently, x-ray diffraction has been used mainly to determine hydrogen positions either indirectly from stereochemical considerations of the ligand disposition about the metals or directly from weak peaks of electron density in difference Fourier maps. The inherent limi-... 

In cathodic addition reactions solvated electrons, radical anions or anions are generated at the cathode and added to activated or unactivated double or triple bonds. This broad spectrum of reactions is partially treated a) in section 8.2 when group conversion generates a reactive intermediate which undergoes addition reactions 1 S5a,b and b) in section 12.2 when olefins are coupled via addition of a cathodically generated radical anion to an activated double bond. 

The wave function of the complex will be a linear combination of the four structures in Figs. 3.5b and c. In a series of olefins, we may expect to see a spectrum of cases. For example, in a series of olefins where the singlet-to-triplet tttt excitation is gradually lowered we may see an increasing metallacyclic character up to complexes, where the C—C distance is that of a single bond. With olefins that are good electron donors, we may see a wave function dominated by a mixture of ionn, and d>nb, while for powerful electron acceptors, we may expect a wave function dominated by d>ion(2) and [Pg.63]

Bromobis[2,3-butanedione dioximato( 1 -)] (4-terf-butylpyridine)cobalt(lIl) is a tan, microcrystalline solid with greatly enhanced solubility in organic solvents compared to the chloro(pyridine) analogue. It is also the compound of choice in preparing alkylcobaloximes by the subsequent procedure because of the ease of isolation of the resultant products. In addition, the bromo(4-ferf-bupy) species react directly with electron-rich olefins, such as ethyl vinyl ether, in the presence of ethanol to yield, in this case, bis[2,3-butanedione dioximato(l-)]-(2,2-diethoxyethyl)(pyridine)cobalt(III).1J Conversion of the dimethyl sulfide compound to the pyridine derivatives is readily detected by a characteristic infrared absorption at 1600 cm 1 (pyridine stretch). The H nmr spectrum of bromobis[2,3-butanedione dioximato(1 -)] (4-ferf-butylpyridine)cobalt (III) has absorptions in the alkane region in the ratio of 3 4 at 6 1.25 ppm [Py—C (CH3)3 ] and 6 2.43 ppm (dh—CH3) from tetramethylsilane. 

However, as we will see later on, other modes of evolution of the primary intermediate radical ions can be suggested to explain some oxidation reactions mediated by electron-transfer processes. In fact, several exceptions to the Foote s BQ-controlled photooxygenation procedure have been reported during the last years on several electron-rich substrates. Thus, the involvement of superoxide ion, as an oxygen active species, in all of the DCA-sensitized photooxygenations, remains questionable [96,105,112,115,128]. Schaap and co-workers [98] recorded under inert atmosphere the characteristic ESR spectrum of the (DCA ) radical anion. On the other hand, the involvement of aryl-olefin radical cations and their reactions with superoxide ion was easily observed by quenching experiments with compounds exhibiting lower oxidation potentials than those of aryl-olefins [85, 95, 98],... 

The transition-metal allyl complexes are air- and temperature-sensitive solids Cr(allyl)3, m.p. ca. 70° Ni(allyl)2, m.p. ca. 0°. The infrared spectrum of both compounds indicates that the bonding of the allyl group to the metal involves r electrons (the olefinic bond appearing at 1520 and 1493 cm.-1, respectively) they can be identified by their mass spectra. 

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