Potential intermediates

The addition of a spillover proton to an adsorbed alkene to yield a secondary carbonium ion followed by abstraction of a proton from the C3 carbon would yield both isomers of 2-butene. The estimated faradaic efficiencies show that each electromigrated proton causes up to 28 molecules of butene to undergo isomerization. This catalytic step is for intermediate potentials much faster than the consumption of the proton by the electrochemical reduction of butene to butane. However, the reduction of butene to butane becomes significant at lower potentials, i.e., less than 0.1V, with a concomitant inhibition of the isomerization process, as manifest in Fig. 9.31 by the appearance of the maxima of the cis- and tram-butene formation rates. 

The oxidation of hydrazine follows the change in surface completely since it oxidizes rapidly on bare nickel and again on the nickel(III) oxide surface but in the intermediate potential region, where the surface is covered with nickel(II) hydroxide, the anodic oxidation cannot occur (Fleischmann etal., 1972d). 

Analogous rearrangements have also been performed by both Fu [73] and Vedejs [105] on (9-acyl benzofuranones and (9-acyl oxindoles to provide synthetic intermediates potentially suitable for elaboration to diazonamide A and various oxin-dole-based alkaloids such as gelsemine respectively. Peris has also examined both Fu s and Vedejs chiral 4-DMAP catalysts for effecting diastereoselective carboxyl migrations of 3-arylbenzofuranones [109]. 

The photolysis of cyclic polysilanes results in ring contraction with concomitant extrusion of a silylene fragment. Although the formation of two reactive intermediates potentially complicates mechanisms for product formation, it has provided a useful method for the synthesis of both unstable and stable disilenes... 

It was commented that In most reactions of complex molecules the intermediate has many more degrees of freedom and so the tendency will be to spend more time near the intermediate potential minimum and, thereby, to lose the directional information in the trajectory , but the model simulation certainly displays a possible role of dynamics effect on chemical reaction. 

Figure I. State energies (a) and qualitative potential energy surfaces (b) for Cr(NH3) +. Alternative mechanistic proposals for (2E)Cr(III) de cay are illustrated in 1(b) a, back intersystem crossing b, direct reaction to yield electronically correlated products c, surface crossing to some ground state intermediate potential energy surface.

Figure 8.6 depicts the four simplest types of unstable periodic orbits for the model CO2 system. Despite the fact that the total energy is well above the dissociation threshold and despite the lack of an intermediate potential well, that could possibly trap the molecule at short distances,... 

The right-hand part of Figure 9.12 depicts the final vibrational state distributions of NO obtained in a three-dimensional wavepacket calculation. They reveal a weak propensity for a final vibrational state n = n — 2. Excitation of vibrational state n in the HONO (Si) complex leads preferentially to NO products in vibrational state (n — 2). Because the intermediate potential well is rather deep, 0.362 eV, the breakup of... 

Scheme 20 Fate of the organometallic intermediate potentially formed during the cyclization of 24...

Hayakawa Y, Nakamura H, Aoki K, Suzuki M, Yamada K, Hirata Y (1971) Synthetic Intermediate Potentially Useful for the Synthesis of Dendrobine. Tetrahedron 27 5157... 

At intermediate potentials (+ 0.8 to - 0. 2 volts) stainless steel becomes passive owing to the formation of stoichiometric M 203 oxides. For lower potentials (lower than -0.2 volts) corrosion takes place again since the oxides are partly reduced before dissolution. At fee lowest potentials (from --0.3 to -0,5 volts) fee corrosion decrease represents the classical cathodic polarization curve. 

Reactions (33) to (37) are equivalent to the overall reaction (31), which mainly occurs at higher electrode potentials (E > 0.8 V/RHE), where the water molecule is activated to form oxygenated species at the catalytic surface, whereas reaction (32) occurs mainly at lower potentials (E < 0.6 V/RHE). At intermediate potentials (0.3 < E <0.1 V/RHE), the dissociative adsorption of water occurs at plurimetallic Pt-based electrodes ... 

---