Among the given compounds, the compound which is most susceptible to a nucleophilic attack at the carbonyl group is:

CH₃COCl

The correct answer is option 1. \(CH_3COCl\).

Let us delve into why acetyl chloride \((CH_3COCl)\) is more susceptible to nucleophilic attack at the carbonyl group compared to the other compounds listed.

Carbonyl compounds, characterized by the \(C=O\) functional group, are susceptible to nucleophilic attack because the carbonyl carbon atom is partially positive due to the strong electronegativity of the oxygen atom. This partial positive charge makes the carbonyl carbon electrophilic, meaning it attracts electron-rich nucleophiles.

Comparison of Compounds:

1. Acetyl Chloride \((CH_3COCl)\):

Acetyl chloride has a carbonyl group \((C=O)\) attached to a chlorine atom \((Cl)\). Chlorine is highly electronegative and withdraws electron density from the carbonyl carbon through the inductive effect. This electron-withdrawing effect makes the carbonyl carbon in acetyl chloride highly electrophilic, enhancing its susceptibility to nucleophilic attack. Nucleophiles are strongly attracted to the partially positive carbonyl carbon, facilitating addition reactions.

2. Acetaldehyde \((CH_3CHO)\):

Acetaldehyde also has a carbonyl group \((C=O)\) but is less reactive towards nucleophiles compared to acetyl chloride. The carbonyl carbon in acetaldehyde is not as electrophilic as in acetyl chloride because it is not as strongly electron-withdrawn.

3. Methyl Acetate \((CH_3COOCH_3\):

Methyl acetate contains an ester group \((RCOOR')\), where R is a methyl group \((CH_3)\). Esters are less reactive towards nucleophiles at the carbonyl group compared to acyl chlorides like acetyl chloride. The carbonyl carbon in esters is less electrophilic due to the resonance stabilization provided by the oxygen atom of the ester group.

4. Methyl Acetoacetate \((CH_3COOCOCH_3)\):

Methyl acetoacetate is a diketone ester, containing two carbonyl groups. While both carbonyl groups can undergo nucleophilic attack, they are generally less reactive compared to acetyl chloride due to resonance stabilization and the presence of electron-donating groups.

Summary:

Acetyl chloride \((CH_3COCl)\) stands out as the compound most susceptible to nucleophilic attack at the carbonyl group among the options provided due to the strong electron-withdrawing effect of the chlorine atom. This effect increases the electrophilicity of the carbonyl carbon, making it highly reactive towards nucleophiles. In contrast, the other compounds listed have carbonyl groups that are either less electrophilic (like acetaldehyde) or stabilized by resonance (like esters), reducing their reactivity towards nucleophiles compared to acetyl chloride.