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0243Pb28an-09.cwk (WP)

0243Pb28an-09.cwk (WP) - B – H BH The apparent resonance...

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Answers to Problem 28, Chemistry 0243 - 2009 CH 2 CH CH 2 H B: CH 2 CH CH 2 BH p K a ~ 38 Why is it possible to deprotonate propene? The resulting anion , and the transition state leading to it, will be stabilized by resonance. Delocalization of charge is a gigantic stabilizing effect. H 2 C C CH 2 CH 2 C H 2 C H H Now look at a modified propene in X . Once again, the molecule cannot be deprotonated by any base. Why not?
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Unformatted text preview: B: – H BH The apparent resonance stabilization of the product anion is an illusion. As the orbitals of the π system and at the bridgehead of the bicyclic system are nearly perpendicular (see Bredt ’ s rule, p.121-122) they do not overlap, and there is no resonance. Thus this “allylic” proton is just as hard to remove as the one in propane....
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