Electron donor ability

Estimation of the influence of end groups by using their topological indexes, Oq and E, has been proposed. The first parameter, Oq, characterizes the shift of the MO modes and the level positions of a PMD containing end groups relative to unsubstituted polymethines. Thus it corresponds to the end-group basicity concept (7). The parameter Oq was found to be related directiy to the electron donor ability 1 = lim ( q. The other index, E,... 

CDCI3, DMSO-d, pyridine-ds), the equilibrium content of the ring-opened form 273 increases with increase in solvent polarity and electron-donor ability of the aryl substituent R. In the sohd, the cyclic tautomers are preferred as proven by IR spectroscopy (97ZOR418). 

The electron-donor abilities of /V-phenyl of dithicno[3,2-A2, 3 v/ pyrrole 24b have been determined using DFT calculations <2005PCA9346>. 

These authors also noted that the electron-donor ability of various derivatives of 2,2-dimesityl-1-phenylethenol decreases in the order enolate > enol > enol silyl ether > enol phosphate > enol acetate. As such, a simple derivatization allows the ready modulation of the electron-donor properties of ends. 

A linear correlation between log Kc of equilibrium 29 and the Hammett equation gives a negative p value (—2.8 0.3), which agrees with the electron donor ability of the amino group of substituted anilines253. 

A depth of this reaction correlates with the electron donor ability of Red and the stability degree of M +(Ox ) complex. The complexation causes anodic shift of metal redox potentials, which reaches almost 100 mV for transition metal cations (Maletin et al. 1979, 1980, 1983). 

BTDM-TTF is one of the most powerfnl donors of the TTF class. Alkylthio-substitution, such as in BEDT-TTF (ET), leads to a slight redaction in its electron-donor ability. Nevertheless, salts of this cation-radical with tetracyanoqninodimethide (TCNQ) and its derivatives show significantly higher conductivity (by ca. 10 -10 ) than the analogons BTDM-TTF salts (Grossel and Weston 1994). This reflects some enhancement of intra and interstack interactions produced by the sulfur atoms at the edges of the donor skeleton. 

Ge), revealed by the AIM study for the X-H-Ni interactions, and the negative sign of the energy density establish the covalent nature of these interactions. These nonclassical species 42 and 43 are particularly stable for X = Si, Ge, which has been attributed to the higher electron-donor ability of these XH3 groups. 

General behaviors are summarized in Table 1. For ligands such as carbon monoxide, isocyanides (CNR), carbynes, nitrosyl NO+ and, although to a smaller extent, nitriles (NCR), which are not only a donors but also good jr acceptors, the net electron-donor ability is modest or poor and the Pl parameter has a high value. However, ligands that are not involved in jt-bonding, such as ammonia (NH3) and pyridine, exhibit lower Pl values that, nevertheless, are usually not... 

The electrical conductivity of TTF TCNQ is of the order of 10 S m at room temperature and increases with decreasing temperature until around 80 K when the conductivity drops as the temperature is lowered. TCNQ is a good electron acceptor and, for example, accepts electrons from alkali metal atoms to form ionic salts. In TTF-TCNQ, the columns of each type of molecule interact to form delocalised orbitals. Some electrons from the highest energy filled band of TTF move across to partly fill a band of TCNQ, so that both types of columns have partially occupied bands. The number of electrons transferred corresponds to about 0.69 electrons per molecule. This partial transfer only occurs with molecules such as tetrathiafulvalene whose electron donor ability is neither too small nor too large. With poor electron donors, no charge transfer... 

The oxygen atom of oxetanes possesses exceptionally high electron donor ability for an ether and appears to coordinate with all electron acceptors that have been investigated. With relatively weak electron acceptors, equilibria can be observed, but with strong electron acceptors the interaction is often so strong that irreversible ring cleavage occurs. 

Studies of hydrogen bonding and iodine complexation on alkyl-substituted oxetanes have shown that 2-alkyl and 2,2-dialkyl substitution enhances the electron donor ability, while 3,3-dialkyl substitution substantially diminishes it. This has been attributed to a decrease in the bond angle strain at the oxygen atom, due to a Thorpe-Ingold effect at C-3, since the effect increases with the size of the alkyl substituent at that position (71BSF4576). 

Protolytic reactions of saturated hydrocarbons in superacid media21 were interpreted by Olah as proceeding through the protonation (protolysis) of the covalent C—H and C—C single bonds. The reactivity is due to the electron donor ability of the <7 bonds via two-electron, three-center bond formation. Protolysis of C—H bonds leads via five-coordinate carbocations with subsequent cleavage of H2 to trivalent ions, which then themselves can further react in a similar fashion ... 

The TT-electron excess of the five-membered rings is accompanied by a high rr-donor character. The best measure of rr-donation is the value of first ionization potential, IP, which for all aromatic heterocycles with one heteroatom of pyrrole type reflects the energy of highest occupied rr-orbital. IP, values decrease in the sequence pyrrole > indole > carbazole furan > benzo[/ ]furan > dibenzofuran thiophene > benzo[/ ]thiophene (Section 2.3.3.9, Tables 21 and 23). Thus, the more extensive the rr-system, the stronger is its electron donor ability. Furan and thiophene possess almost equal rr-donation, which is considerably lower than that of pyrrole. 

On increasing the electron-donor ability of the substituents on the phenyl rings the stability of the NiL2(RNNR) complexes is going to decrease. With the 2,2 -azapyridine a complex has been reported for nickel(0) for which a polymeric structure (47) has been suggested.210... 

The nonbonding level of unsubstituted polymethines is the lowest vacant one in cations and the highest occupied one in anions. The nonbonding MO modes fall on odd atoms, and the other frontier MO has its modes on even atoms. As a rule, an attachment of end groups causes the frontier level shifts. A parameter, (pQ, called electron donor ability, has been proposed for quantitative estimation of the position of the frontier levels (16) ... 

Electron Level Position. One essential condition of spectral sensitization by electron transfer is that the LUMO of the dye be positioned above the bottom of the conduction band, eg, e > —3.23 eV inAgBrore > —4.25 eV in ZnO (108). To provide the desired frontier level position respectively to the valence and conduction bands of the semiconductor, it is necessary to use a polymethine with suitable electron-donor ability (pQ. Increasing the parameter CpQ leads to the frontier level shift up, and vice versa. Chain lengthening is known to be accompanied by a decrease of LUMO energy and hence by a decrease of sensitization properties. As a result, it is necessary to use dyes with high electron-donor ability for sensitization in the near-ir. The desired value of CpQ can be provided by end groups with the needed topological index 0 or suitable substituents (112). 

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