0
$\begingroup$

chlorobenzene structure

McMurry says that halogens are deactivating the benzene aromatic ring, but in contrast, -OH group in phenol is (strongly) activating the ring. So I- in halogens is much stronger than I- in -OH group? Why? Oxygen is more electronegative than e.g. chlorine.

$\endgroup$
3
  • $\begingroup$ chemistry.stackexchange.com/questions/38341/… $\endgroup$
    – Mithoron
    Commented May 5 at 18:20
  • $\begingroup$ I don't think it can be explained with some rules of thumb expected in questions like this. Disubstituted oxygen's lone pair is more available for bonding than of any single bonded halide. Why is that? On your level of chem-fu... it just is. $\endgroup$
    – Mithoron
    Commented May 5 at 18:26
  • $\begingroup$ @Mithoron Hi, thanks for the reply! But I have read a lot about molecular orbitals and quantum chemistry, so if you know something about this, could you just drop a literature here? Thanks a lot again :) $\endgroup$ Commented May 5 at 18:35

1 Answer 1

1
$\begingroup$

Think about the lone pairs of halides. In case of fluorine, it is 2p-orbitals, in case of chlorine, it is 3p-orbitals and so on. Benzene, being an aromatic compound, interacts with electron-donating and withdrawing groups via its 2p-orbitals. The 3p-orbitals simply do not have the correct size to overlap with the 2p-orbitals of benzene significantly. Thus, despite it being more electronegative, the +M-effect of fluorine is actually much stronger.

Literature: Clayden, Warren, Greeves. Organic Chemistry. Oxford University Press Inc., New York, p. 280.

$\endgroup$
0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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