Inductive Effect: Why Does Charge Decrease?

[Karan Punjabi]

Guys, I just understand that what is inductive effect but I'm not getting the reason that why as chain increases the positive charges on each carbon atom after 3 or 4 bonds decreases or becomes negligible?

 

[Dr. Courtney]

Not sure what the question is.

 

[Karan Punjabi]

Not sure what the question is.

Consider n-pentyl chloride on 1 carbon atom which is attached to chlorine atom there is a partial positive charge and on second carbon atom it is said that there is less positive charge and as we move further we get more less positive charge. So why?

 

[CrazyNinja]

Lets name the carbons to make it easier. The carbon attached to chlorine is A, the next one B... and so on.

Now the positive charge on A is generated by highly EN chlorine. It is not a complete positive charge mind you, because the electron pairs A shares with B compensate for this charge. Now the partial shifting of the electron pair A-B (electron pairs shared by A and B) towards generates a partial negative charge on B. This charge will be smaller than that on A because it is not generated due to a highly EN atom, but by another partial positive charge (which itself is weak). From B to C, the charge decreases further and we generally neglect inductive effect after 3-4 carbons.

 

[Karan Punjabi]

Lets name the carbons to make it easier. The carbon attached to chlorine is A, the next one B... and so on.

Now the positive charge on A is generated by highly EN chlorine. It is not a complete positive charge mind you, because the electron pairs A shares with B compensate for this charge. Now the partial shifting of the electron pair A-B (electron pairs shared by A and B) towards generates a partial negative charge on B. This charge will be smaller than that on A because it is not generated due to a highly EN atom, but by another partial positive charge (which itself is weak). From B to C, the charge decreases further and we generally neglect inductive effect after 3-4 carbons.

I understood you but I was going for the fact that the partial positive charge on Carbon A is having the same capacity to attract shared pairs of electrons as chlorine atom because the partial positive charge is generated due to chlorine.

 

[CrazyNinja]

Sorry for the delay in answering.

Yes you are right that chlorine generates the partial positive charge. But this charge is not as strong as chlorine because its effect is suppressed by the movement of bond pair A-B. Chlorine can attract shared pairs as it is its fundamental property (being so EN). Carbon is attracting only because it has a partial charge. This charge is not sufficient enough to polarise carbon B as much as chlorine polarises carbon A.

 

[Karan Punjabi]

That means there are two factors for carbon i.e its electronegativity and positive charge on it

 

[CrazyNinja]

Yes. But its own EN doesent olay a role when it is bonded to another carbon. C-C bonds don't have polarity.