Basically, I've recently been thinking about using HSAB theory to rationalize the concept of michael donors and michael acceptors. Essentially, if we have a deprotonated diketone (with a lone pair on the alpha position carbon) or the Gilman reagent, it attacks the carbon in a vinylic ketone in a 1,4 addition.
However, if we used a Grignard reagent, than it attacks the carbonyl carbon in a 1,2 addition.
How can we use HSAB theory to justify this? I've figured out that the carbonyl carbon's LUMO is the pi-star orbital while the vinylic carbon center's LUMO is also the pi-star orbital except with the carbon bonded to another carbon, thus it should be higher in energy than a pi star orbital bonded with an oxygen.
I've also figured that the carbon nucleophile center on a Michael donor (such as that of the diketone) should be "softer" than the nucleophile center on a Grignard reagent's carbanion because the charge is less concentrated due to resonance and thus the HOMO of the Michael donor is not as high as the HOMO of a Grignard reagent.
However, I do not know where to go from here. Can someone help me what I'm doing wrong?