Hello,
so, in other words the lone pair of C is higher in energy than the lone pair of N and therefore the HOMO of the nucleophile is the lone pair of C that attacks the LUMO of the carbonyl compound?
I have however found that in Sn1 reactions where CN is involved , when the carbocation is produced, the harder end of the CN ( N end) attacts the carbocation
while in Sn2 reactions the softer end ( the C end) attacks the carbon from which the leaving group will depart.
In the Sn1 case, electrostatic forces are involved and therefore the carbocation is referred as a hard electrophile ( and the attacking N-end of CN is referred as hard).
In the Sn2 case, the C-X ( X is the leaving group) bond is not very polarized and therefore it is a soft electrophile (the attacking C end of CN is thereby soft).
The fact that the carbonyl group is a hard electrophile should mean that the hard end of CN ( the N end) should attack it, or it does not apply here?
thank you very much