Inductive electron-withdrawing groups

Attack distai to electron-withdrawing group (inductive effect)... 

A tertiary carbonium ion is more stable than a secondary carbonium ion, which is in turn more stable than a primary carbonium ion. Therefore, the alkylation of ben2ene with isobutylene is much easier than is alkylation with ethylene. The reactivity of substituted aromatics for electrophilic substitution is affected by the inductive and resonance effects of a substituent. An electron-donating group, such as the hydroxyl and methyl groups, activates the alkylation and an electron-withdrawing group, such as chloride, deactivates it. 

Since the (n-Bu)3Sn radical (R ) is nucleophilic (17), a partial negative charge must be produced at the methine carbon whose chlorine is being abstracted. The rate of this abstraction should clearly be enhanced by electron-withdrawing groups on R due to their stabilization of this charge by inductive effects. As observed, the removal of Cl from EW (or W diad) is expected to be more facile than from EVE (or VE diad) as a result of a -halogen effect in the former structure. 

The effect of introducing electron-withdrawing groups, e.g. Cl, N02, close to a basic centre is to decrease the basicity, due to their electron-withdrawing inductive effect (cf. substituted anilines below, p. 70) thus the amine... 

Electron-withdrawing substituents Inductive effect (o) Increased by purely inductive effect Decreased in penicillins due to neighboring-group [76]... 

Analogous effects can be observed with substituted phenols, the presence of electron-withdrawing groups in the nucleus increasing their acidity. In the case of a nitro substituent, the inductive effect would be expected to fall off with distance on going p-... 

This effect is increased if there is a suitable electron-withdrawing group in the ortho or para position on the aromatic ring. Thus, p-nitroaniline and o-nitroaniline have pATa 1-0 and —0.3 respectively. These aromatic amines are thus even weaker bases than aniline, a result of improved delocalization in the free base. The increased basicity of the ortho isomer is a result of the very close inductive effect of the nitro group the meta isomer has only the inductive effect, and its is about 2.5. 

It may also be concluded from the interaction scheme that the properties of [3.3.3]cyc-lazines are very sensitive to inductive perturbations. Aza substitution as well as introduction of electron withdrawing groups in the active positions 1, 3, 4, 6, 7 and/or 9 lowers the energy of the HOMO, leaving that of the LUMO unchanged. A stabilizing effect by these perturbations is to be expected together with a dramatic influence on the NMR and UV spectra. 

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