Electronic activation

Another approach is spin-coupled valence bond theory, which divides the electrons into two sets core electrons, which are described by doubly occupied orthogonal orbitals, and active electrons, which occupy singly occupied non-orthogonal orbitals. Both types of orbital are expressed in the usual way as a linear combination of basis functions. The overall wavefunction is completed by two spin fimctions one that describes the coupling of the spins of the core electrons and one that deals with the active electrons. The choice of spin function for these active electrons is a key component of the theory [Gerratt ef al. 1997]. One of the distinctive features of this theory is that a considerable amount of chemically significant electronic correlation is incorporated into the wavefunction, giving an accuracy comparable to CASSCF. An additional benefit is that the orbitals tend to be... 

Although a hydroxyl group strongly activates an aromatic ring toward electrophilic attack an oxyanion substituent is an even more powerful activator Electron delocaliza tion m phenoxide anion leads to increased electron density at the positions ortho and para to oxygen... 

The structure on the left is biradical, while the two others are ionic, corresponding to both electrons being at the same carbon. The simplest CASSCF wave function which qualitatively can describe this system has two electrons in two orbitals, giving the three configurations shown above. The dynamical correlation between die two active electrons will tend to keep them as far apart as possible, i.e. favouring the biradical structure. Now... 

The electrons involved in the actual reaction (which are designated here by dots and referred to here as the active electrons) can be treated according to the general prescription of the four-electron three-orbital problem with the VB wave functions (Ref. 5)... 

The correction to the relaxing density matrix can be obtained without coupling it to the differential equations for the Hamiltonian equations, and therefore does not require solving coupled equations for slow and fast functions. This procedure has been successfully applied to several collisional phenomena involving both one and several active electrons, where a single TDHF state was suitable, and was observed to show excellent numerical behavior. A simple and yet useful procedure employs the first order correction F (f) = A (f) and an adaptive step size for the quadrature and propagation. The density matrix is then approximated in each interval by... 

Mayoral, M.L., Atsmon, D., Gromet-Elhanan, Z. Shimshi, D. (1981). Effect of water stress on enzyme activities in wheat and related wild species Carboxylase activity, electron transport and photophosphorylation in isolated chloroplasts. Australian Jourrml of Plant Physiology, 8, 385-94. 

Two positions in (50) (a and b) are equally activated electronically. Experiments showed that (49) was in fact the major product from the Friedel-Crafts... 

As mentioned above, ferrocene is amenable to electrophilic substitution reactions and acts like a typical activated electron-rich aromatic system such as anisole, with the limitation that the electrophile must not be a strong oxidizing agent, which would lead to the formation of ferrocenium cations instead. Formation of the CT-complex intermediate 2 usually occurs by exo-attack of the electrophile (from the direction remote to the Fe center. Fig. 3) [14], but in certain cases can also proceed by precoordination of the electrophile to the Fe center (endo attack) [15]. 

Huzinaga, S. (1995) 1994 Polanyi Award lecture Concept of active electrons in chemistry. Canadian Journal of Chemistry, 73, 619-628. 

An extraordinary way of stabilizing RUO2-coated CdS colloids for H2 generation was chosen by Fendler and co-workers The colloidal particles were generated in situ in surfactant vesicles of dioctadecyldimethylammonium chloride and dihexa-decyl phosphate. Thiophenol as a membrane permeable electron donor acted as a sacrificial additive. Later, a surface active re-usable electron donor (n-C,gH3,)2N — (CHj)—CH2—CHj—SH, Br was incorporated into the vesicles. Its R—SS—R oxidation product could be chemically reduced by NaBH to regenerate the active electron donor. The H2 yields in these systems were only 0.5 %. However, yields up to 10% were later reported for a system in which CdS was incorporated into a polymerizable styrene moiety, (n-C,jH3jC02(CH2)2) N (CH3) (CH2CgH4CH=CH2>, CP, and benzyl alcohol was used as the electron donor. 

For substituted benzenes, ring activators (electron-releasing groups) increase sensitivity and ring deactivators (electron-withdrawing groups) decrease sensitivity (exception halogenated benzenes)... 

As the contribution of the 5s and 5p orbitals of Ba to Wd is quite significant [43] for the BaF molecule, we have included these orbitals of Ba in our Cl active space for the calculation of Wd and p(, for the ground state of the BaF molecule. The occupied orbitals above the 25th are also included in the RASCI space from energy consideration. Thus altogether 17 active electrons (9a and 8(3) are included in the Cl space. The present calculations for Wd consider nine sets of RASCI space, which are constructed from 17 active electrons and 16, 21, 26, 31, 36, 46, 56, 66, and 76 active orbitals to analyze the convergence of Wd. 

In order to investigate the single electron donation process from a reduced flavin to a pyrimidine dimer or oxetane lesion, the photolyase model compounds 1-4 depicted in Scheme 4 were prepared [41, 42]. The first model compounds 1 and 2 contain a cyclobutane uracil (1) or thymine (2) dimer covalently connected to a flavin, which is the active electron donating subunit in photolyases. These model systems were dissolved in various solvents... 

Neutron activation Electron spectroscopy for chemical analysis (ESCA)... 

A few examples of cycloadditions between nitroalkenes and vinyl ethers without the use of Lewis acids have been reported (Eq. 8.105), in which additional activating electron-withdrawing groups are generally required.161... 

Apparently the same reaction sequence takes place when THPO and Re(o-phen)(CO)3C1 are electrolyzed in acetonitrile at room temperature. The electrolysis replaces only the first activated electron transfer step of the CIEEL mechanism. 

A more recent publication by Weigand and Pelka has disclosed a polymer-bound Buchwald-Hartwig amination [40], Activated, electron-deficient aryl halides were coupled with conventional PS Rink resin under microwave irradiation. Subsequent acidic cleavage afforded the desired aryl amines in moderate to good yields (Scheme 7.22). Commercially available Fmoc-protected Rink amide resin was suspended in 20% piperidine/N,N-dimethylformamide at room temperature for 30 min to achieve deprotection. After washing and drying, the resin was placed in a silylated microwave vessel and suspended in dimethoxyethane (DME)/tert-butanol... 

The active electron bound state (r-/ ) satisfies the Schrodinger equation... 

Many active electronic devices can be operated at cryogenic temperatures [45], They are generally of the field-effect transistor (FET) type and are based on silicon (working down to 100K) or gallium arsenide (working even below 4K). 

At room temperature thermally activated electron transfer occurs from the bpy ligand to the remote pyridinium site followed by decay of the lower, pyridinium-based CT state. The electron transfer step is the intramolecular analog of the paraquat quenching of Ru(bpy)32+. ... 

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