ek orgo a-b unstaurated carbonyls

[johnj7]

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This comes from the Exam krackers, 7th edition organic chemistry book by Jonathan Orsay. (I hope i can quote like this)

on pg 61, it talks about a-b unsaturated carbonyls
it says
"additionally the electron withdrawing carbonyl group pulls electrons from the carbon-carbon double bond and makes the B-carbon less susceptible to attack by a nucleophile (electrophilic addition). Thus rather than the nucleophile adding to the B-carbon, it may sometimes add to the oxygen atom, forming the enol-keto tautomers."

I'm a bit confused on the wording on this one
when it says "B-carbon less susceptible to attack by a nucleophile (electrophilic addition)" is it referring to the fact that the double bond between the B and A carbon does not want to undergo electrophilic addition, because if it does, then a the B-carbon will have a + charge, which is bad because the C=O is e-withdrawing.... thus the B-carbon is less susceptible to "nucleophilic" attack?

also, how does a nucleophile add to the oxygen atom? don't only electrophiles like hydrogen add to oxygen?

thank you for any response!

 

[ChexMix]

Sorry for bringing this back, but I am reading the same part of the book right now and it is really bothering me. TPR says the beta carbon IS very electrophilic and most nucleophiles attack the beta carbon.

In a,b-unsaturated carbonyl compounds, where does the Nucleophile attack first?

Thanks so much for your help!

 

[Doodl3s]

Yea, EK was weird about this (and damn this thread is old lol, i feel bad no one answered the poor kid)

According to the stuff i learned IN orgo, which i trust more, in alpha-beta unsaturated, the nuclephile is added to the beta carbon. The electrons are pushed onto the alpha carbon which gets protonated. It's called the Michael reaction.