[fadingrainbows]

While looking through my notes for revision, I found the following:
Carbonyl compounds give nucleophilic rather than electrophilic addition reactions because electrophilic addition would give an intermediate with a + charge on the carbon, which is described as 'more likely' than an intermediate with a - charge on the oxygen, which occurs in nucleophilic addition.
Is there actually a reason why the formation of one intermediate should be more likely than the formation of the other, or is this a badly phrased arguement that the second mechanism is more likely due to the greater stabilty of the intermediate?

[Donaldson Tan]

draw the MO diagram for the carbonyl group.  You should be able to see the HOMO is on the carbon atom, and not the oxygen atom. This is why the carbonyl group acts as an electrophile, and not a nucleophile. Hence, the carbonyl group is susceptible to nucleophilic addition.