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Consider the molecule 1-chloroethane

enter image description here

Let carbon attached to $\ce{Cl}$ be $\ce{C1}$ and other one be $\ce{C2}$. While learning inductive effect I was told that $\ce{Cl}$ due to high electronegativity pulls the $\ce{C1–Cl}$ bond electrons towards itself leading to development of partial positive charge on $\ce{C1}$ and partial negative charge on $\ce{Cl}$ .Now this $\ce{C1}$ which has became a little electron-deficient tries to pull electron of the adjacent adjacent carbon $\ce{C2}$ leading to development of a further smaller partial charge on $\ce{C2}$. I have following doubts:

  1. Will $\ce{C1}$ only pull electrons from $\ce{C2}$ or from the hydrogen atom attached to it also. I think it does pull, but then why don't we take that pull into consideration?

  2. When $\ce{C1}$ pulls electrons from $\ce{C2}$, the partial positive charge developed on it due to the pull of electrons by the chlorine atom will be reduced a little but why do we then show $\ce{C1}$ to have same partial positive charge?

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    $\begingroup$ Kindly see this and use mathjax again, Thanks! chemistry.meta.stackexchange.com/questions/86/… $\endgroup$
    – Rishi
    Jun 27, 2021 at 5:40
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    $\begingroup$ The effect exists but is very small and insignificant. $\endgroup$ Jun 27, 2021 at 6:20
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    $\begingroup$ Is not the inductive effect taken as the relative effect of atom/group, compared to hydrogen ? By other words, a bound hydrogen is taken as the reference zero by definition. $\endgroup$
    – Poutnik
    Jun 27, 2021 at 13:24
  • $\begingroup$ @Poutnik do you mean the same as first line in the given link en.wikipedia.org/wiki/… $\endgroup$
    – Lalit
    Jun 27, 2021 at 13:30
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    $\begingroup$ @Lllt No, I want to say that inductive effect of the methyl group or the chlorine atom is compared to inductive effect of hydrogen, if it was there instead of them. $\endgroup$
    – Poutnik
    Jun 27, 2021 at 15:44

1 Answer 1

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I will show you how I understand this effect. I like to think that partial positive charge on $\ce{C1}$ attracts the electrons from $\ce{C2}$ because of the electrostatic force. With this model your questions can be answered this way:

  1. Yes, $\ce{C1}$ will pull electrons from every adjacent atom, including hydrogen. It may pull them, however, to less extent from hydrogen because it has less electrons than carbon (or rather alkyl group), and smaller charge will result in weaker attraction according to our model.
  2. What you are saying is right. The reason why we still write just $\delta +$ instead of some kind of $0.7\delta +$ is mostly convenience. This writing can be used in organic chemistry to show mechanisms, for example, and in this case we don't need super-accuracy in determining the magnitude of the charge itself (like it could be in some physical model), we just need to show that it is positive. It will be different in every case (molecule) and calculating the exact charge seems like waste of time, but we still are aware of the inductive effect, although don't explicitly show it.
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  • $\begingroup$ thankyou for replying. I completely understood the answer of my second question. I'm having few doubts related to first one but ,why does small size of hydrogen cause Carbon to pull electrons to a less extent from it $\endgroup$
    – user108965
    Jun 27, 2021 at 6:33
  • $\begingroup$ Oh, sorry, I am formulating my sentences not in the best way. Actually, what I misinterpreted as two things is just one — carbon has more electrons. It is the same as the first one because larger atoms have more electrons in them (this is also how dispersion forces are explained). And what you have is that higher charge means greater attraction and electrons are pulled with greater force from carbon than from hydrogen. $\endgroup$
    – Azamat
    Jun 27, 2021 at 7:07
  • $\begingroup$ @Azamat Hydrogen has less electrons than carbon, why will this fact cause carbon to pull electrons from it to a less extent $\endgroup$
    – Lalit
    Jun 27, 2021 at 8:05
  • $\begingroup$ @Lllt, it's the electrostatic force. The law is $F = k \ \frac{q_1 q_2}{r^2}$. Let's say that $q_1$ is the charge of $\ce{C1}$ carbon, the force now depends on the charge $q_2$. If there are more electrons around, this charge is greater, therefore the force is also greater. There are more electrons at the carbon (because it has another hydrogens from which to take them), so the force is greater. However, I don't think that this gives a huge difference between the carbon and hydrogen, and teachers should actually note the effect on hydrogen too. $\endgroup$
    – Azamat
    Jun 27, 2021 at 8:21

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