See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Reactivity of acyl derivatives toward nucleophilic acyl substitution depends on the electrophilicity of the carbonyl carbon. This is governed by two factors: (1) the electron-withdrawing or electron-donating ability of the leaving group substituent, and (2) the stability of the leaving group (i.e., how good a leaving group it is). Step 1: Identify the three acyl derivatives. - Compound 1: An ester (CH3C(=O)OCHCH3) — the leaving group is an alkoxide (RO-). - Compound 2: An acid chloride (CH3C(=O)Cl) — the leaving group is Cl-. - Compound 3: An amide (CH3C(=O)NHCH3) — the leaving group is an amine (RNH-). Step 2: Assess the electron donation by resonance into the carbonyl. - In amides, nitrogen donates its lone pair strongly into the carbonyl by resonance (nitrogen is a better electron donor than oxygen or chlorine by resonance), making the carbonyl carbon least electrophilic. - In esters, oxygen donates its lone pair into the carbonyl by resonance, but less effectively than nitrogen (oxygen is more electronegative, lone pair less available). - In acid chlorides, chlorine donates very little by resonance (poor pi overlap due to size mismatch of 3p orbital with 2p of carbon), and Cl is strongly electron-withdrawing inductively, making the carbonyl most electrophilic. Step 3: Assess leaving group ability. - Cl- is an excellent leaving group (weak base, stable anion). - RO- (alkoxide) is a moderate leaving group (stronger base than Cl-). - RNH- (amine) is a poor leaving group (strong base, high pKa of conjugate acid ~35-38). Step 4: Combine both factors to rank reactivity toward nucleophiles. - Acid chloride (2): Most reactive — least resonance donation + best leaving group. - Ester (1): Intermediate reactivity — moderate resonance donation + moderate leaving group. - Amide (3): Least reactive — strongest resonance donation + worst leaving group. Order of increasing reactivity (least to most): 3 < 1 < 2 Why other options fail: - (a) 1 < 2 < 3: Incorrect — amides are less reactive than esters. - (c) 1 < 3 < 2: Incorrect — amides are less reactive than esters, not more. - (d) 2 < 1 < 3: Incorrect — acid chlorides are most reactive, not least. Therefore, the correct answer is B.