OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2018: Question 2

✅ Correct Answer: C

Compound C features a carbonyl group ( C=O ) directly attached to a nitrogen atom, which defines an amide functional group. Furthermore, the nitrogen atom is bonded to one hydrogen atom ( H ), one methyl group ( CH₃ ), and the carbonyl carbon, making it a secondary amide (N-substituted amide).

💡 Key Knowledge: Classifying Amides & Amines

• Amide linkage: Contains a carbonyl group ( C=O ) bonded to a nitrogen atom ( -C(=O)-N< ).
• Primary amide ( -CONH₂ ): Nitrogen is bonded to 0 carbon chains (2 hydrogens).
• Secondary amide ( -CONHR ): Nitrogen is bonded to 1 carbon chain/group (1 hydrogen).
• Tertiary amide ( -CONR₂ ): Nitrogen is bonded to 2 carbon chains/groups (0 hydrogens).
• Amines vs Amides: Amines contain -C-N bonds without the adjacent C=O carbonyl group.

🧠 Exam Technique

Approach structural multiple-choice questions systematically in two steps:

1. Identify the core functional group: Look for the C=O connected to N to eliminate non-amides.
2. Count nitrogen substituents: Look at what else is attached directly to the nitrogen atom to determine the degree of substitution.

❌ Common Errors & Distractor Analysis

• A & B (Incorrect): These structures contain a carboxylic acid group ( -COOH ) and an amino group ( -NH- or -N(CH₃)₂ ) separated by a -CH₂- spacer. They are amino acids/derivatives, not amides, because the nitrogen is not directly adjacent to the C=O .
• D (Incorrect): While compound D is an amide (has C=O attached to N ), the nitrogen is bonded to two methyl groups and has zero hydrogens, making it a tertiary amide instead of secondary.