Inductive effect is introduced in many textbooks by giving an example of an alkyl halide $R-X$.

The bond C1-X is polar due to electronegativity difference, therefore X gains partial negative charge ∆(-), and C1 gains partial positive ∆(+). Due to some deficiency of electrons in the C1 , C2-C1 bond becomes polar and above process is repeated.

So by this point of view, if we take $R-Li$, as C1-Li bond is polar, Li gains ∆(+) and C gains ∆(-) and above thinking process is repeated again.

Thus we can conclude that Carbon chain can act as both +I and -I depending upon the situation on hand.

So why do we always consider an alkyl chain to be a +I group?

Example, if on a carbon chain, there is a carbanion, we still consider alkyl group to be +I, but it should have been the opposite.

  • $\begingroup$ This is going to be a redundant question...I thought this confusion would be finally answered :( $\endgroup$ – B.Anshuman May 6 '20 at 17:24
  • $\begingroup$ Well, is the $C-Li$ bond an organic bond? $\endgroup$ – Firefox1921 Jun 20 '20 at 19:57
  • $\begingroup$ @Firefox1921, what do you mean by 'organic bond'? $\endgroup$ – B.Anshuman Jun 20 '20 at 22:20
  • $\begingroup$ Also if you aren't satisfied with C-Li, we can take C-B (boron) as well, or even a carbanion attached to alkyl group. $\endgroup$ – B.Anshuman Jun 20 '20 at 22:21
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    $\begingroup$ I think that inductive effect is a relative concept, it depends on the type of substituents attached to the carbon chain. As Li is more electropositive compared to C or C is more electronegative with respect to Li. So, R group shows -I effect and Li shows +I effect. $\endgroup$ – Manu Jun 21 '20 at 2:45

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