Electron-releasing inductive effect

Electron donating (or electron releasing) inductive effect... 

The carbon atom with the odd electron is an electron-deficient site. Alkyl groups attached to such a C have an electron-releasing inductive effect which attenuates the electron deficiency, thereby stabilizing the radical. 

If the electronegativity of the atom or group of atoms attached to the carbon chain is less than the electronegativity of the carbon then the displacement of electrons takes place away from group along the C-chain and this effect is called the Electron Releasing Inductive Effect or (+I)-Effect. This inductive effect can be represented as shown below ... 

The high negative value of p indicates that the reaction is strongly accelerated by groups with electron-releasing inductive effects (negative a ). In the sequence CH2 (OC2 Hs )2 rate coefficient is increased by approximately 3.5 powers of ten for each substitution of H by CH3 in the alpha position. This strong inductive effect and the complete absence of steric hindrance can be taken as evidence for an A1 mechanism [177]... 

We know how to estimate the stability of a carbonium ion, on the basis of inductive effects and resonance. Because of the electron-releasing inductive effect of alkyl groups, stability and hence rate of formation of the simple alkyl cations follows the sequence 3 > T > l ... 

For alkyl substituents, the electron-releasing inductive effects of the alkyl group relative to CH3 are substantial, i.e., up to 2.3 kcal mole for t-Bu, but nonetheless, these are three to seven times smaller than the corresponding predominant polarizability (P) effects. The values of / are nearly additive in the two series Me, Et, i-Pr, and t-Bu and Et, CH2CHF2, and CH2CF3. However, P values show that saturation occurs in the former series (increments of 3.8, 2.7, and 2.0 kcal mor ), and in the latter series P is approximately constant. 

Baker-Nathan effect. Effect originally observed in the reaction of p-substituted benzyl bromides with pyridine and other processes in which the observed rates are opposite to those predicted by the electron-releasing inductive effect of alkyl groups, i.e., CH3 > CH3CH2 > (CH3)2CH > C(CH3)3. To explain it, a type of electron delocalization involving 2 electrons was proposed, termed hyperconjugation, which manifests itself in systems in which a saturated carbon atom attached to an unsaturated carbon or one with an empty orbital bears at least one hydrogen atom. 

Polarization of this C—C bond by the electron-releasing inductive effect of the sf carbon of the methyl group destabilizes this contributing structure... 

In mass spectrometry, the knowledge of inductive effects allows an analyst to understand (and perhaps anticipate) the evolution of an ion. As an example. Figure 9.3 shows the transfer of a hydride ion (H ) on a carbon initially carrying a positive charge. Such a transfer is thermodynamically favorable since it transforms a mono-substituted carbocation weakly stabilized by an alkyl chain into a very stable carbo-cation trisubstituted by alkyl groups with electron-releasing inductive effects. 

One cleavage leads to the formation of an m/z 72 ion (a,), the other to the formation of an m/z 58 ion (o ). The m/z 72 ion is stabilized better than the m/z 58 ion because the electron-releasing inductive effect of the isopropyl group is superior to that of the ethyl group. One must not deduce that the formation of the m/z 72 ion is favored. This amounts to neglecting the stability of the radicals formed during these alpha ruptures. 

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