Substituents electronic

Although Noyce and Fike have recently found for the solvolysis of 2-thiazolyl-ethyl chlorides analogous modality of substituent electronic effect transmission from position 2 toward position 5 and from position 5 toward position 2(60). a more general conclusion indicates that the... 

Reactions of substituted cumyl benzoates in 50 50 trifluoroethanol-water show no effect of [NaN3] on the rate between 0 and 0.5 M. The product ratio, however, is highly dependent on the cumyl substituent. Electron-releasing substituents favor azide formation whereas electron-withdrawing substituents result in solvent capture. Formu-... 

For cyclopentanone, cyclohexanone, and cycloheptanone, the K values for addition are 48, 1000, and 8 M , respectively. For aromatic aldehydes, the equilibria are affected by the electronic nature of the aryl substituent. Electron donors disfavor addition by stabilizing the aldehyde whereas electron-accepting substituents have the opposite effect. 

Substituted arylamines can be either more basic or less basic than aniline, depending on the substituent. Electron-donating substituents, such as — CH3, -NH2, and -OCH3, which increase the reactivity of an aromatic ring toward electrophilic substitution (Section 16.4), also increase the basicity of the corresponding arylamine. Electron-withdrawing substituents, such as —Cl, -NO2, and -CN, which decrease ring reactivity toward electrophilic substitution, also decrease arylamine basicity. Table 24.2 considers only -substituted anilines, but similar trends are observed for ortho and meta derivatives. 

Reaction 31 appears to be little affected by substituent electronic effects or by steric effects of either sulfonyl chloride or styrenes. Treatment of /5-chlorosulfones with triethylamine in benzene affords the corresponding a, /5-unsaturated sulfones in excellent yield. The copper-catalyzed addition of sulfonyl iodides to simple and cyclic alkenes has also been exploited76. 

Styrenes may act as 2n and 4n components of the Diels-Alder reaction depending on the substitution site and the electronic effects of the substituent. Electron-donating groups at the a-carbon of the olefinic double bond enhance the dienic reactivity of styrenes [30]. 

In 5-aryl-4-hexenols with ERG substituents, electronic factors outweigh the exo... 

The decarboxylation of mercuric 3- and 4-nitro-l,8-naphthalene-dicarboxylates has been studied to determine substituent electronic effects [Eq. (83)] (95,96), since significant steric effects are unlikely. There is disagreement over the products. In an early study, 3- and 4-nitro-l,8-naphthalenedicarboxylates were found to undergo decarboxylation predominantly in the ring without the nitro group (95), consistent... 

M effects consistent with the interaction depicted in 95. The extent of the pd-7r-bonding seems to vary with the substituents, electron withdrawal being greatest in aldehydes, less in esters, and least in acetals.243 (See also Section XII,B,5.)... 

The conductance of the OPE nitro-16 (X = N02) was monitored by the STM-BJ method, as the nitro group was reduced to NO and NH2, and then protonated to NH3. The resulting data gave an inverse linear Hammett plot with the meta-cr substituent parameter, indicating that substituent electron release into the aromatic core increases conductance [63]. 

Examples of the application of correlation analysis to diene and polyene data sets are considered below. Both data sets in which the diene or polyene is directly substituted and those in which a phenylene lies between the substituent and diene or polyene group have been considered. In that best of all possible worlds known only to Voltaire s Dr. Pangloss, all data sets have a sufficient number of substituents and cover a wide enough range of substituent electronic demand, steric effect and intermolecular forces to provide a clear, reliable description of structural effects on the property of interest. In the real world this is not often the case. We will therefore try to demonstrate how the maximum amount of information can be extracted from small data sets. 

Shifts for meta carbon atoms remain almost unaffected by all kinds of substituents, unlike shifts for ortho and para carbons. Electron-releasing substituents (electron donors) increase tt electron densities in ortho and para positions and thereby induce a shielding relative to benzene (Sc(o,p) < 128.5 ppm)22. Electron-withdrawing groups (electron acceptors), on the other hand, decrease the ortho and para jr electron densities and lead to a deshielding relative to benzene (Sc(o,p) > 128.5 ppm). 

A substantial divergence from the behaviour described up to now occurs with the 2,6-(V,(V-tetramethyl anilines (Table 7). The effect of the para substituent is no longer systematic, and no good correlation with substituent electronic properties is displayed. Evidently, the extent of nitrogen lone-pair delocalization in these compounds reflects a balance between electronic demand for, and steric inhibition of, delocalization that varies with the individual compounds. Nitrogen chemical shifts are a sensitive probe for these effects. 

Although Christ51 examined 170 shifts of some substituted nitrobenzenes 35 years ago, only at the beginning of the following decade did systematic studies of the substituent effects on 170 chemical shifts appear in the literature with the first reports52,53 of substituted anisoles, acetophenones and benzaldehides. The potential of this probe as a measure of substituent electronic effects was demonstrated. 

The enantioselectivity increases dramatically when the ligands contain electron-withdrawing P-aryl substituents. Electron-donating substituents on the substrate give the highest ee (91% for 6-methoxy-2-vinylnaphthalene in apolar solvents). Mechanistic studies at room temperature have shown that at low concentration of HCN nickel zero species are the resting states, but at higher concentrations of HCN q3-benzyl nickel cyanide species were also observed. 

Reduction potenhals of ketones and aldehydes are effected by the substituents. Electron-withdrawing groups usually facilitate the electroreduction of these compounds [1, 2]. Electroreduction of aliphatic and aromatic ketones and aldehydes generally takes place under mild reaction conditions however, the nature... 

Aldehydes are generally more reactive than ketones in nucleophiUc addition reactions due to steric and electronic reasons. Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one such substituent. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophUicity of the carbonyl carbon more effectively than in former. 

The regioselectivity for the ene pathway, in the photooxidation of several para substituted /3,/3-dimethylstyrenes, was recently found to depend on the electronic nature of the aryl substituents . Electron-withdrawing substituents, such as p-CFs or p-F,... 

NMR analysis does not provide an accurate estimate of the proportions of oxepin and benzene oxide present at ambient temperature due to a fast rate of isomerization (on the NMR timescale). The oxepin-benzene oxide ratio was found to be dependent upon solvent, temperature, substituents (electronic and steric effects) and the resonance energy of the molecule. 

Extensive work on the interaction of aromatic compounds with xenon difluoride has been carried out in order to investigate the reaction mechanism and the scope of the fluorination depending on the substituents electronic nature.26-59 62 It has been found that benzene and substituted aromatics react with xenon difluoride at room temperature in the presence of hydrogen fluoride to form the typical products of electrophilic fluorination contaminated with low quantities of difluoro-substituted molecules. 

Regioselective substitutions in di- and tri-halogenopyrimidine derivatives can in many cases be achieved. Chloro, bromo, and iodo substituents undergo aminolysis at approximately the same rates whereas a fluoro substituent reacts 60-200 times faster. 4(6)-Halo substituents react up to 10 times faster than 2-halo substituents. Electron-donating substituents (e.g., Me, Ph, OMe, NMe2) decrease the rate of aminolysis whereas electron-withdrawing substituents (Cl, CF3, N02) have the opposite effect (B-94MI602-01). 

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