Question

"Lack of reactivity of alpha-halocarbonyl compound in Sn1 reaction" - Explain.

Answer 1

Even more effective is conjugation with electron deficient p bonds [in this case, the orbitals it can conjugate with are electron deficient, and so stabilise the negative charge even better]. The most important example is that of the carbonyl group. a-halo carbonyl compounds display the fastest SN2rates.

What is effectively happening is that the $p^*$ of the C-C bond and the $s^*$ of the C-Br bond (both low energy) combine with each other to form an even lower energy $p^* + s^*$ orbital. The nucleophile will then attack where this new orbital has the largest coefficients (in the usual place). Attack could occur at the carbonyl, but it would be reversible.