Question

During hydrolysis of methyl chloride and acetyl chloride by aqueous NaOH interaction starts by overlapping between respectively

• A. σ (filled) - σ* (vacant) and σ (filled) - π* (vacant)
• B. σ* (vacant) - σ (filled) and σ (filled) - π (vacant)
• C. σ (filled) - σ (vacant) and σ (filled) - π (vacant)
• D. σ (vacant) - σ (fill13ed) and σ (filled) - π (filled)

Answer 1

Answer: (A)

σ (filled) - σ* (vacant) and σ (filled) - π* (vacant)

Answer 2

The hydrolysis of methyl chloride ($\text{CH}_3\text{Cl}$) by aqueous $\text{NaOH}$ is a nucleophilic substitution reaction. The nucleophile is the hydroxide ion ($\text{OH}^-$), which has filled orbitals (lone pairs). The electrophile is methyl chloride, where the carbon atom bonded to chlorine is electrophilic. In an $\text{SN}2$ reaction, the nucleophile attacks the carbon atom from the backside relative to the leaving group (chlorine). This attack involves the overlap of a filled orbital of the nucleophile ($\text{OH}^-$) with the vacant antibonding $\sigma^*$ orbital of the $\text{C-Cl}$ bond. The filled orbital of the nucleophile (a lone pair on oxygen) can be considered as having $\sigma$ symmetry with respect to the axis of attack. Thus, the interaction starts by overlapping between a σ (filled) orbital of the nucleophile and a σ* (vacant) orbital of the substrate ($\text{CH}_3\text{Cl}$).

The hydrolysis of acetyl chloride ($\text{CH}_3\text{COCl}$) by aqueous $\text{NaOH}$ is a nucleophilic acyl substitution reaction, proceeding via an addition-elimination mechanism. The nucleophile is the hydroxide ion ($\text{OH}^-$), which has filled orbitals. The electrophile is acetyl chloride, specifically the carbonyl carbon, which is highly electrophilic. The nucleophile attacks the carbonyl carbon. This attack involves the overlap of a filled orbital of the nucleophile ($\text{OH}^-$) with the vacant antibonding $\pi^*$ orbital of the $\text{C=O}$ double bond. The filled orbital of the nucleophile (a lone pair on oxygen) can be considered as having $\sigma$ symmetry with respect to the axis of attack on the carbonyl carbon. Thus, the interaction starts by overlapping between a σ (filled) orbital of the nucleophile and a π* (vacant) orbital of the substrate ($\text{CH}_3\text{COCl}$).

Therefore, during the hydrolysis of methyl chloride and acetyl chloride by aqueous $\text{NaOH}$, the interaction starts by overlapping between respectively:

• For methyl chloride: σ (filled) - σ* (vacant)
• For acetyl chloride: σ (filled) - π* (vacant)