[Kalibasa]

My professor gave us a handout on hybridization that is much denser than what was in the book, and I'm having trouble deciphering it! There was a description of bond dissociation energies and s-character that I finally understood- basically, that  in determining bond strength, the stability of the radicals formed in homolysis is more important than the actual strength of the bond broken (and how much s character it has). Then my handout says this:

"Similarly the s character of the orbital containing the lone electron pair will influence the stability of the anion, and therefore, the pKa value of the hydrocarbon precursors of this anion.  If the geometry of the hydrocarbon is similar to that of the anion, the more s character in the hybrid making the "acidic" C-H bond, the lower the pKa value of the hydrocarbon (and the more stable the anion)."

I really don't understand this. If there is more s-character in the "acidic" C-H bond, wouldn't that make it stronger and thus harder to break? Why would more s-character lead to a *lower* pKa in the hydrocarbon? And I think I see how they're relating it to what came before... (just as bond strength depends more on the stability of the radicals in homolysis than the actual bond broken, the acidity of the hydrocarbon depends on the stability of the anion it would create)... is that right? But then I still don't understand why increased s character in the hydrocarbon bond would lead to a more stable anion.

If someone can help me translate this into English , I'd be really grateful! Thanks, and sorry this was so long!!

[ArchStanton]

Hi

S-orbitals, as I am sure you know, offer a higher probability of finding an electron close to the nucleus than an equivalent shell level P-orbital.

So, more s charcater in an anion means the electrons will have a greater probability of being near to the nucleus. Being close to the positively charged nucleus will offer a more stable anion.

This means SP3>SP2>SP in terms of PKa.

Hope this helps.