[a student]

hi
I have a molecule and in my book( heterocyclic chemistry by Gilchrist, page 68 ) it has shown that Nu will attack the carbonyl rather than chlore, but I think Nu must attack chlore because it's bond must be weaker.
here is the reaction, can you tell me what the reason is.

[orgopete]

In general, many reactions have kinetic and thermodynamic reactions that may be taking place and may differ. If a kinetic reaction is fast but reversible, we may not be aware of it taking place. Examples are additions to carbonyl compounds. In writing reaction mechanisms, we write the enolization of an ester for a Claisen reaction and ignore the addition to a carbonyl group. If you used the alkoxide of a different ester, we would know that an addition does take place as ester exchange would also occur.

In this example, we should not be surprised that an addition to a carbonyl takes place. The question that we might ask is at which rate does each reaction take place? Let's consider a haloform reaction. I argue that we don't find a new mechanism of attack at the carbonyl group at the end of the reaction, but more likely a change in the rates of attack. Carbonyl group addition is likely occurring throughout the reaction. However, if the addition is reversible, we may not be aware of it occurrence. Furthermore, the rate of attack probably increases as the electron donating properties of a  methyl group are changed into an electron withdrawing trihalomethyl group. Since the trihalomethyl group can pull electron density away from the tetrahedral alkoxide intermediate, it can become a leaving group and reveal that additions have been occurring to the carbonyl group.

However, if isotopic atom labeling were done, we should find that even a compound like acetone will exchange the isotopic oxygen label as well as the hydrogens on a methyl group. I don't know the relative rates however.