Electron-withdrawing power of the

The interaction between a substituent and the ring carbon to which it is bonded could be related to some electronic characteristics of the unsubstituted ring and especially to the net charge of its various sites. In that respect the rr-net charges diagram discussed in Section 1.5 indicates that the electron-withdrawing power of the ring-carbon atoms will decrease in the order, 2>4>5. 

All the halogenothiazoles, depending on the electron-withdrawing power of the halosubstituent, together with the electron-withdrawing power of the azasubstituent, are only slightly susceptible to electrophilic substitution reactions such as nitration, sulfonation, and so on, while the polyhalogenatjon reaction can take place. 

Carboxylic acids are weak acids and m the absence of electron attracting substituents have s of approximately 5 Carboxylic acids are much stronger acids than alcohols because of the electron withdrawing power of the carbonyl group (inductive effect) and its ability to delocalize negative charge m the carboxylate anion (resonance effect)... 

The electron-withdrawing power of the tnfluoromethyl group in the 2,2,2-tri-fluoroethyl ether of 9-hydroxy-9-(dinitromethyl)fluorene considerably retards its hydrolysis compared with simple alkyl ethers [59] (equation 57)... 

This effect is observable within a series of very similar electrophiles. Zollinger27 found that in reactions of diazonium ions substituted with 4-C1, 3-C1, and 3-N02 substituents (i.e. the reactivity and electron-withdrawing power of the ion increased along the series) the respective kinetic isotope effects were 6.55, 5.48 and 4.78. 

In this case, the enol form is not more stable than the keto form (115). The enol form is less stable, and converts to the keto form upon prolonged heating. It can, however, be kept at room temperature for long periods of time because the tautomerization reaction (12-3) is very slow, owing to the electron-withdrawing power of the fluorines. 

What this implies is that given one equilibrium constant for addition of a nucleophile of known 7 to a carbonyl compound, one could estimate the equilibrium constant for addition of another nucleophile to the same carbonyl compound. This requires knowing the slope of the plot of log K versus y this slope is not very sensitive to the nature of the carbonyl compound, but it is at least known that A H2o/ MeOH depends on the electron-withdrawing power of the groups bonded to the carbonyl, and thus more information is needed to estimate an equilibrium constant for strongly electron-withdrawing substituents. From Ritchie s studies of nucleophile addition to trifluoroacetophenone," we can derive a slope for log K versus 7 of 0.42, distinctly less than the value of 1 for formaldehyde or simple benzaldehydes. 

As previously mentioned above, the chiral recognition abilities of the phenyl-carbamates of polysaccharides are greatly influenced by the substituents on the phenyl groups. In order to evaluate the effect of the substituents on the interaction between CSPs and solutes, the retention times of acetone and the first-eluted isomer of l-(9-anthryl)-2,2,2-trifluoroethanol (39) on 3- and 4-substituted CSPs are plotted against the Hammett parameter a of the substituents (Figure 3.33).130 The retention times of acetone tend to increase as the electron-withdrawing power of the substituents increases, whereas those of the first-eluted isomer of 39 tend to decrease. These results indicate that... 

Agrawal and co-workers reported the synthesis of two tetrazole-based explosives, namely, 5-picrylamino-l,2,3,4-tetrazole " (PAT) (149) and 5,5 -styphnylamino-l,2,3,4-tetrazole (SAT) (150) from the reaction of 5-amino-1,2,3,4-tetrazole (148) with picryl chloride and styphnyl chloride respectively. These explosives have been studied for their thermal and explosive properties. The thermal stability of SAT (exotherm peak at 123 °C) is lower than PAT (exotherm peak at 185 °C), which is possibly attributed to the decreased electron-withdrawing power of the picryl group by being attached to two tetrazole units. PAT and SAT have calculated VODs of 8126 m/s and 8602 m/s respectively. ... 

The value of the pKa in CTAB is much lower than that in SDS (Table 1). This is true for both the acid and ester forms of the complexes. Further, there is a significant difference in the pKa between the acids and esters of the heme complexes (see Table 1). It is interesting that this difference is largest in the neutral TX-lOO ( 1.0) as compared to that in SDS and in CTAB ( 0.6). There is also a trend in the variation in pKa with substitution at 2, 4 positions of the porphyrin i.e. ethyl proton > vinyl (Table 1). This trend is qualitatively the reverse of the trend in the strength of electron withdrawing power of the substituents. 

Pyridines are reduced more easily than the corresponding benzenoid compounds. The greater the electron-withdrawing power of the substituents attached to the pyridine ring the easier is reduction by nucleophilic reducing agents. 

Nitration of l-methyl-2-phenylquinol inium sulfate with nitric acid gives l-methyl-2-(m-nitrophenyl)quinolinium sulfate (97%), indicative of the marked electron-withdrawing power of the charged quinolinium system. 

Aromatic carboxylic acids are, in general, less reactive towards sulfur tetrafluoride than aliphatic acids. The reactivity strongly depends on the nature of the aromatic ring substituents. Benzoic, 4-methylbenzoic and particularly 4-methoxybenzoic acid (la-c) give poor yields of the respective (trifluoromethyl)benzenes 2a-c, but the yields of 2 increase with increasing electron-withdrawing power of the substituents.122 Yields of (trifluoromethyl)benzenes substantially increase, even under milder conditions, in the presence of an excess of anhydrous hydrogen fluoride.123... 

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