Electrophilic behavior

Methanol oxidation on Ag polycrystalline films interfaced with YSZ at 500°C has been in investigated by Hong et al.52 The kinetic data in open and closed circuit conditions showed significant enhancement in the rate of C02 production under cathodic polarization of the silver catalyst-electrode. Similarly to CH3OH oxidation on Pt,50 the reaction exhibits electrophilic behavior for negative potentials. However, no enhancement of HCHO production rate was observed (Figure 8.48). The rate enhancement ratio of C02 production was up to 2.1, while the faradaic efficiencies for the reaction products defined from... 

The remarkable NEMCA behavior of the isomerization reaction is shown in Fig. 9.31. At potentials negative with respect to the open circuit potential ( 0.38V) the rates of cis- and tram-2-butene formation start to increase dramatically. At a cell voltage of 0.16 to 0.10V the observed maximum p values are 38 and 46, respectively. The absolute A values are approximately equal to 28, as computed from the ratio Ar/(I/F) (with I/F presenting the rate of proton supply to the catalyst). The system thus exhibits a strong non-faradaic electrophilic behavior. 

Figure 12.5. Ethylene oxidation on Pt finely dispersed on Au supported on YSZ.7 Effect of the current 1 on x 1, where x is the time constant measured during a galvanostatic transient experiment with I as the applied current x is obtained by fitting either r/r0=exp(-t/x) or l-exp(-t/x) to the experimental data depending on the sign of the current and whether the reaction is electrophilic or electrophobic, (a) Positive values of I for electrophilic (squares, T=371°C, pO2=18.0 kPa, Pc2H4=0-6 kPa) and electrophobic behavior (circle, T=421°C, p02=l 4.8 kPa, Pc2H4 CU kPa) (b) negative currents, electrophilic behavior (T=421°C, p02=14.8 kPa, pC2H4=0.1 kPa. Reprints with permission from Academic Press.

Much of the literature regarding dihalocarbenes is concerned with reactions of CX2 with olefinic substrates to give 1,1-dihalocyclopropane derivatives. These reactions occur with retention of stereospecificity, as expected for singlet carbenes. Dihalocarbenes also exhibit strong electrophilic behavior towards olefins, and will often not react with weakly nucleophilic species if stronger nucleophiles are present. 

Interestingly, copper(I) salts also catalyze the cyclopropene-vinylcarbene isomerization [681]. In this case the transient carbene complexes again show electrophilic behavior, behavior similar to that of the complexes formed from copper(I) salts and diazoalkanes or sulfonium ylides. 

It has been argued that this rearrangement may occur via a bond-switch process in 167. In this process the sulfur acts as a nucleophilic center, which is opposite to the electrophilic behavior of the pivotal sulfur in, for example, the conversion of 149 into 150. The alternative intermediacy of a bipolar sulfur tetra-azapentalene structure or a ring-opened intermediate in... 

Only one example of electrophilic behavior of silicon-stabilized lithiooxiranes is reported. Intermolecular C—Li insertion followed by Li20 elimination occurs by raising the temperature, and ( ) vinylsilanes are obtained stereoselectively (Scheme 80). Reaction of lithiooxiranes with aluminum , zirconium and silicon reagents leads to the corresponding ate complexes, which undergo 1,2-metallate rearrangements. 

In contrast to the examples reported above, some other aryl- and vinyl-stabilized lithiooxiranes show a strong electrophilic behavior and undergo rearrangement reactions (Scheme 83, see also Section V.A.2.a for other examples). Lithiated styrene oxide has been engaged in 1,2-metallate rearrangement with zirconacycles . 

Bottomley, F. (1978). Electrophilic behavior of coordinated nitric oxide. Acc. Chem. Res. 11, 158-162. 

In addition to forming dimers with double-bond-like character that can participate in cycloaddition-type reactions, the reconstruction of the (100) semiconductor surface is also responsible for the presence of electrophilic and nucleophilic sites. The bond of a tilted dimer deviates from the plane of the surface, and the resulting structure of each dimer consists of an up dimer atom protruding from the surface and a down dimer atom recessed on the surface. The electron density at the up atom of the dimer is higher than that at the down atom, leading to nucleophilic and electrophilic behavior, respectively [49]. 

A novel illustration of the electrophilic behavior of coordinated NO+ is provided in a recent report by Feltham (226) in which the specifically labeled nitro nitrosyl complex m-Fe(15N0)(14N02)(S2CNMe2)2 was found to undergo an intramolecular oxide transfer according to (102). 

Two recent papers by Schug and Guengerich (233b,c) present additional examples of the electrophilic behavior of nitrosyl in [Ru(NO)(NH3)5]3 +. One of these (233c) shows the conversion of NO+ to an organic nitrile via a sequence similar to (104)—(106). 

Aggarwal and coworkers have studied the electrophilic behavior of enantiomerically pure N-p-toluenesulfinimines and N-tert-butanesulfinimines in the asymmetric Baylis-Hillman reaction with methyl acrylate with and without Lewis acids [26], In the presence of In(OTf)3 good yields and high diastereoselectivities have been achieved providing an effective route to /i-amino-a-methylene esters. 

W[CH(PMe3)CH—C(0)Me] appeared in 1984 (203). This electrophilic behavior is reminiscent of Fischer carbene reactions (204). 

The cytotoxicity of several benzo-annulated iso-a-carbolines (369-372, 377, 378, 380) has been studied in vitro on human tumor KB cells (Table X) 136). The linear ellipticine analog 371 is 10 times more active than ellipticine (1) in this screen. As was mentioned earlier, this derivative also displays significant in vivo activity against P388, L1210, and B16 implanted mouse tumors TIC values 190, 175, and 224%, respectively). The resemblance of the imine grouping of these iso-a-carbolines to ellipticine quinone imine 6 is obvious. It will be of interest to see how the electrophilic behavior of these compounds compares to that of the quinone imines. 

The reactions of O3 with C3H6, 9 and 10, were based on a review of the mechanism of ozonolysis by Murray (15). The accepted mechanism in the gas phase is similar to that commonly referred to as the Criegee mechanism in the liquid phase. The attack of O3 on C3H6 is electrophilic, and Vrbaski and Cvetanovic (16) have correlated the electrophilic behavior with that of oxygen atom-olefin reactions. Both reaction rates correlate with the ionization potentials of a series of olefins. 

A still broader definition of acids has been put forward by Usanovich (57), who identifies electrophilic behavior with acids and nucleophilic behavior with basicity. An acid... 

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