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Topic: I Don't Understaand  (Read 2037 times)

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Offline abhistud

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I Don't Understaand
« on: September 08, 2017, 11:28:01 AM »
Refer to the picture given below. So, it says that since in haloarene, carbon is sp2 hybridised, it has more s character and thus better electronegativity. Okay! That sounds fine to me. Now, it says that since it's more electronegative, it holds the electron's a tad bit more. But, isn't that opposing the attraction of electrons towards the chlorine atom thus reducing the polarity and making the bond less stable. I don't UNDERSTAAAND!

Offline Babcock_Hall

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Re: I Don't Understaand
« Reply #1 on: September 08, 2017, 05:43:20 PM »
I think its fine to say that greater s-character leads to shorter, stronger bonds.  The (homolytic) bond dissociation energy for the C-Cl bond in chlorobenzene is greater than it is in chloromethane (400 kJ versus 352, in the table in my textbook).  Speaking only for myself, I am hesitant to bring electronegativity into the discussion.

I would not go so far as to say that bond strength is entirely uncorrelated with chemical reactivity, but I would not explain reactivity in this way, to the exclusion of other factors.  For example, compounds such as chlorobenzene cannot undergo SN2 substitutions at least partially because the geometry of the transition state cannot be achieved.  This geometrical requirement does not apply to other kinds of substitution reactions.

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