1as Cl is better leaving groupas the negative charge on Cl is stablised by its hifh electronegativity and Large size due to which negative charge is diffused

The most susceptible to nucleophilic attack at the carbonyl group is:

1) CH3COCl
2) CH3COOCH3
3) CH3CONH2
4) CH3COOCOCH3

Explanation:

Nucleophilic attack at the carbonyl group occurs when a nucleophile, which is an electron-rich species, attacks the electrophilic carbon of the carbonyl group. The susceptibility of a compound to nucleophilic attack depends on several factors, including the nature of the carbonyl group and the presence of electron-donating or electron-withdrawing groups.

1) CH3COCl:
The carbonyl group in CH3COCl is an acyl chloride, which is highly reactive towards nucleophilic attack due to the presence of the highly electronegative chlorine atom. The electronegativity of chlorine withdraws electron density from the carbonyl carbon, making it more electrophilic and therefore more susceptible to nucleophilic attack.

2) CH3COOCH3:
The carbonyl group in CH3COOCH3 is an ester, which is less reactive towards nucleophilic attack compared to acyl chlorides. The presence of the electron-donating methoxy (-OCH3) group attached to the carbonyl carbon increases the electron density around the carbon, making it less electrophilic and therefore less susceptible to nucleophilic attack.

3) CH3CONH2:
The carbonyl group in CH3CONH2 is an amide, which is also less reactive towards nucleophilic attack compared to acyl chlorides. The presence of the electron-donating amino (-NH2) group attached to the carbonyl carbon also increases the electron density around the carbon, making it less electrophilic and less susceptible to nucleophilic attack.

4) CH3COOCOCH3:
The carbonyl group in CH3COOCOCH3 is a carboxylic acid anhydride, which is more reactive towards nucleophilic attack compared to esters and amides. The presence of two carbonyl groups increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack.

In summary, among the given compounds, the most susceptible to nucleophilic attack at the carbonyl group is CH3COCl, followed by CH3COOCOCH3. The presence of electron-withdrawing groups such as chlorine increases the electrophilicity of the carbonyl carbon, making it more reactive towards nucleophilic attack. Conversely, the presence of electron-donating groups decreases the electrophilicity of the carbonyl carbon, resulting in lower reactivity towards nucleophilic attack.