Acidity inductive electron withdrawal

The effects of fluonnation on carbanion stability are largely deduced from C-H acidity data (p. 988) [64], a-Halogens stabilize carbanions in the order Br > Cl > F, which IS opposite the inductive electron-withdrawing order and reflects the... 

The inductive effect in 4-hydroxybenzoic acid is electron withdrawing, but this is a modest effect compared with the electron-donating resonance effect. This significantly destabilizes the conjugate base, and 4-hydroxybenzoic acid (p a 4.6) is less acidic than benzoic acid. The last example, 4-acetylbenzoic acid, is the most acidic of the group, and this is primarily the result of an electron-withdrawing resonance effect, though there is also a favourable inductive effect. 

Steric effects on the reactivity of benzoic acid derivatives are a little more complicated. The first significant point is that the aromatic carboxylic acids and esters are often some two orders of magnitude less reactive than the corresponding aliphatic compounds. Chapman et al. 7, have explained this difference in terms of three co-operative factors (i) the stabilization of the initial state by delocalization in the case of the aromatic compounds, (ii) inductive electron-withdrawal by the ring, which is significant in esterification... 

Several examples were discussed earlier of the use of substituent effects for the elucidation of the mechanisms of silene reactions with nucleophilic reagents. For example, the trends in the rate constants for reaction of the series of 1,1 -diarylsilenes 19a-e with alcohols, acetic acid, amines, methoxytrimethylsilane and acetone all indicate that inductive electron-withdrawing substituents at silicon enhance the reactivity of the Si=C bond, and are consistent with a common reaction mechanism in which reaction is initiated by the formation of an intermediate complex between the silene and the nucleophile. 

The positively charged nitrogen acts as an inductive electron-withdrawing group and therefore makes the carboxylic acid group a stronger acid. 

Tin boron exchange reactions provide a convenient route to diborylated acetylene (equation 33). Diborylalkynes show an enhanced Lewis acidity in comparison to dibory-laUcanes as demonstrated by the coordination of THF in (31), but a lack of binding to the related alkyldiborane (32). This effect has been attributed to the stronger inductive electron-withdrawing effect of sp-hybridized relative to sp -hybridized carbons. ... 

The acidity of HA increases when inductively electron-withdrawing groups are attached to A and decreases when inductively electron-donating groups are attached to A (cf. CC13C02H with CH3C02H, and HOH with EtOH). 

F5SOOSF5 is difficult, after the initial publication in 1962 this chemistry has, unfortunately, not been explored further. Physicochemical studies on p-pentafluoro-sulfuranyloxybenzoic acid (p/Q = 5.04 for comparison, benzoic acid 5.68, p-nitro-benzoic acid 4.55) show the p-OSFj group has a relatively large ffp , , value of +0.44 (for comparison, p-F +0.062, p-COOEt +0.45), indicating a strong inductive electron-withdrawing (-/) effect. 

The sialic acid structure incorporates a carboxylate at the anomeric centre, which can be inductively electron donating in its deprotonated form and inductively electron withdrawing when protonated, as well as deoxygenation of the position next to the anomeric centre. These features make sialosyl cations more stable than simple aldopyranosyl cations, and hydrolysis and solvolysis reactions have been investigated using the substrates shown in Figure 3.24. 

The inductive electron-withdrawal of chlorine in 3-chloropyridine causes an increase in the acidities of the hydrogen atoms in the 2- and 4-positions. It is difficult to predict which proton will be preferentially abstracted by a given base. The... 

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