Which one of the following reactions does not involve the donation of an electron pair?

A) $\ce{H+ + CH3NH2 -> CH3NH3+}$

B) $\ce{AlCl3 + Cl- -> AlCl4-}$

C) $\ce{CH3Cl + CN- -> CH3CN + Cl-}$

D) $\ce{Cl2 + 2I- -> 2Cl- + I2}$

The answer is D, but I don't know why.

The equation could be split into two half equations:

$\ce{Cl2 +2e- -> 2Cl-}$

$\ce{2I- -> I2 + 2e-}$

But surely this shows the iodide ion is donating a pair of electrons to the chlorine atom?

I'm sure really what approach I should take for this question.


D donates 2 electrons, not an "electron pair." There is a subtle but important difference here because D is a reaction that takes place via the transfer of single electrons (though in the end, 2 are transferred in total).

So, A, B, and C are examples of Lewis acid-base neutralizations, but D is not. D is classical redox reaction.

  • $\begingroup$ How could one differentiate between the two (electron donor and electron pair donor) ? $\endgroup$
    – doubleOrt
    Jan 18 '19 at 7:45
  • $\begingroup$ Mechanistic studies, or in most cases, pattern recognition. $\endgroup$
    – Zhe
    Jan 18 '19 at 12:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.