Inductive electron donation

The half-wave reduction potentials for a series of annelated 1,4 naphthoquinones (102-106) increase upon alkylation, and decrease as ring size decreases (Table 13). The more cathodic reduction potentials of 2,3-dimethylnaphtho-l,4-qui-none (106, 0.846 V) and l,2,3,4-tetrahydro-9,10-anthroquinone (105,0.854 V) as compared to 1,4-naphthoquinone (0.685 V) are expected from inductive electron donation of alkyl groups. A decrease in reduction potential from 105 to 2,3-cyclobutanaphtho-l,4-quinone (103) (0.695 V) as ring size decreases is observed such that the reduction potential of 103 is only slightly higher than the parent 1,4-naphthoquinone. 

On the basis of this equation Zou et al. have concluded that hydrophobic compounds with inductively electron-donating ortho substituents would be favorable for the activity [193]. In continuation of this, Zou and coworkers have carried out CoMFA-based 3D-QSAR analysis of these compounds together with 5-[l-aryl-l,4-dihydro-6-methylpyridazin-4-one-3-ylj-2-arylamino- 1,3,4-oxadiazoles [ 194]. Here also the antifungal activity of these compounds has been found to be well explained by their steric and electrostatic properties. In addition to this, it has confirmed the bioisosterism... 

Dienophiles are activated by electron-withdrawing substituents. Alkyl groups, by means of inductive electron donation and steric effects, tend to reduce the rate of cycloaddition. 

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). 

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 presence of an inductively electron-donating alkyl group resulted in formation of the ketone alone, while the geometrically more constrained cyclohexylidine 72c gave exclusively the cyclisation product. This suggests that the oxidation of intermediates 72 is influenced by inductive effects as well as geometric considerations. 

There are two ways substituents can donate electrons into a benzene ring inductive electron donation and electron donation by resonance. There are also two ways substituents can withdraw electrons from a benzene ring inductive electron withdrawal and electron withdrawal by resonance. 

An inductive effect is often cited as the reason why f-BuOH is less acidic than EtOH. Actually, t-BuOH is less acidic than EtOH not because t-Bu is an inductive electron-donating group but because it is much more difficult to solvate the very hindered t-BuO and partly neutralize its negative charge than it is to solvate EtO. In fact, in the gas phase, where solvation plays no role, f-BuOH is more acidic than EtOH. Solvent effects play a very important role in determining acidity in the liquid phase, where most chemists work, but they are often ignored because they are difficult to quantify. 

---