Number of electrons donated

When hydroxypteridines are considered, it must be borne in mind that these compounds exist principally in the pteridinone forms, containing thermodynamically stable amide functions, and consequently have low reactivity. Their stability towards acid and alkali correlates well with the number of electron-donating groups which apparently redress the deficit of ir-electrons located at the ring nitrogen atoms. Quantitative correlations can be seen in the decomposition studies of various pteridinones (Table 7). These results are consistent with the number of the oxy functions and their site at the pteridine nucleus. The... 

The Fricdel-Crafts type polyalkylation of alkyl-substituted benzenes with 3 becomes easier and faster as the number of electron-donating methyl groups on the phenyl group increases. This is consistent with the fact that the alkylation occurs in the fashion of electrophilic substitution. The tendency of starting incthylben-zenes to form reoriented products also increases in the same order from toluene to mesitylene. 

Compound Number of electrons donated by the ligands Experimental number of metal-metal bonds dCo-Co> (A), (bonding) dCo-Co> (A). (non-bonding) Ref. 

We have studied the dependence of the oxidation peak potentials on the substitution in the rings A and B for 16 structurally different 2-hydroxychal-cones [61]. The increase in the number of electron donating groups in ring B resulted in the decrease of the peak potentials while the peak potentials remain virtually the same when the munber of electron-donating groups in ring A was... 

The normality, N, of a redox reagent is n times the molarity, where n is the number of electrons donated or accepted by that species in a chemical reaction. 

Framework dectrcxK (F) apn] tbc number of metal valence electrons (M) plus the number of electrons donated by kgands (L) minus twelve (F = M + L — 12). 

One of the oldest linkers for amides is the (4-methylbenzhydryl)amine linker (MBHA Entry 1, Table 3.11). In contrast to the corresponding benzhydrol linker (which is cleavable by 5% TFA in DCM, 5 min [45]), acidolysis of the benzylic C-N bond of the MBHA linker requires treatment with hydrogen fluoride or a similar acid. As for A-benzylamides, the acid-lability of Al-(diarylmethyl)amides increases with the number of electron-donating substituents on the aryl groups. 

Benzyl ethers bearing electron-donating groups can be cleaved by treatment with acids or oxidants. The rate of solvolysis increases with the number of electron-donating groups, and in the series benzyl < benzhydryl < trityl. For the solid-phase synthesis of oligonucleotides, the 5 -hydroxyl group is usually protected as 4,4/-dimethoxytrityl... 

Conversion increases from toluene to p-xylene to p-methoxytoluene due to the electron-donating effects of the substituents. The increased number of electron-donating substituents creates a positive charge on the reaction center and activates the ring for increased oxidation rates. This effect is in agreement with the radical cation oxidation mechanism proposed by Som-rani et al. (1995). Electron density on the reaction center was shown to play an important role in determining oxidation rates of toluenes. 

It is observed that the reactivity of the KA increases as the number of electron-donating substituents on the olefin increases. Steric hindrance leads to a decreasing reactivity. The authors rationalized the formation of the photoadduct as follows (see Scheme 12). First, the radical ion pair 49 is formed by single electron transfer between photoexcited 3C6o and the electron rich ketene silyl acetal fol-... 

The global utility of this H-NMR alkyne probe is decreased by the scarcity of terminal alkyne adducts relative to the abundance of internal alkyne adducts. Diphenylacetylene and dimethylacetylenedicarboxylate (DMAC) are two particularly popular alkyne ligands which have no acetylenic proton to monitor. An empirical correlation between alkyne irx donation and, 3C chemical shift for the bound alkyne carbons has been recognized (155) which partially fills this spectroscopic need. A plot of alkyne 13C chemical shifts, which span over 100 ppm (Tables II and III), versus N, the number of electrons donated per alkyne to fulfill the effective atomic number guideline, reveals both the advantages and the limitations... 

Increasing number of electron-donating R groups Increasing carbocation stability... 

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