1,4-nucleophilic addition vs. 1,2-nucleophilic additions

[lDanny]

Hi,

Just wondering if I got this straight. 1,2-nucleophilic additions is when the Nu attacks the carbonyl. 1,4-nucleophilic additions is when Nu attacks the conjugated end carbon, like in a Michael reaction.

Doesn't 1,2 need a conj. system? Why does the Nu in the Michael rxn attack the beta carbon instead of the carbonyl? Is it because the beta carbon is resonance stablized? Thanks.

I think I need a sleep, all of these concepts are getting mixed up in my head..lol (2:30am).

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[loveoforganic]

I've seen 1,2 Addition defined as both direct addition to a carbonyl regardless of whether or not conjugation is present as well as when you add to the "same" double bond in a conjugate polyene.

As far as why one nucleophile will attack at the carbonyl carbo. And another will add at the beta position, that's way beyond the scope of the mcat. If you'd like to learn about it though, look into hard and soft acids and bases theory (hsab)