9. Proton NMR of ethyl acetate will show
a. Three peaks, singlet-doublet-triplet in 3:2:3 intensity ratio
b. Three peaks, singlet-quartet-triplet in 3:2:3 intensity ratio
c. Three peaks, doublet-quartet-triplet in 2:2:3 intensity ratio
d. Four peaks, singlet-quartet-triplet-doublet in 3:2:3:2 intensity ratio

Proton NMR of Ethyl Acetate: CSIR NET Solved MCQ with Detailed Analysis

Ethyl acetate exhibits three distinct signals in its proton NMR spectrum: a singlet, quartet, and triplet with 3:2:3 integration ratio. The correct answer is option b.​​

Structure Breakdown

Ethyl acetate (CH₃COOCH₂CH₃) has three proton environments:

• CH₃-COO (acetyl methyl, 3H, ~2.0 ppm, singlet—no adjacent H).​​

• -OCH₂- (methylene, 2H, ~4.1 ppm, quartet—split by 3H on CH₃ via n+1 rule).​​

• -CH₃ (terminal methyl, 3H, ~1.3 ppm, triplet—split by 2H on CH₂).​​
  This yields three peaks in 3:2:3 intensity, matching the classic ethyl ester pattern.​

Option Analysis

• a. Three peaks, singlet-doublet-triplet (3:2:3): Incorrect. No doublet exists; CH₂ splits into quartet (n=3), not doublet (n=1).​

• b. Three peaks, singlet-quartet-triplet (3:2:3): Correct. Matches exact splitting (singlet for isolated CH₃, quartet for CH₂ next to CH₃, triplet for terminal CH₃) and integration.​​

• c. Three peaks, doublet-quartet-triplet (2:2:3): Wrong. No doublet; acetyl CH₃ is singlet (3H), not 2H doublet, and ratios mismatch.​

• d. Four peaks, singlet-quartet-triplet-doublet (3:2:3:2): Incorrect. Only three environments, not four; no extra doublet.​