A primary amide is generally represented by the formula

Analysis

The question asks for the general chemical formula of a primary amide. In organic chemistry, amides are derivatives of carboxylic acids where the hydroxyl group (-OH) is replaced by an amino group (-NH₂).

Concept Explanation

To identify the correct formula, we look at the nitrogen atom attached to the carbonyl group (C=O):

• Primary Amide: The nitrogen atom is attached to only one carbon atom (the carbonyl carbon) and two hydrogen atoms. Its general structure is RCONH₂.
• Secondary Amide: The nitrogen atom is attached to the carbonyl carbon and one other alkyl group (R). Its general structure is RCONHR.
• Tertiary Amide: The nitrogen atom is attached to the carbonyl carbon and two other alkyl groups (R). Its general structure is RCONR₂.

Step-by-Step Solution

1. Identify the functional group: The amide functional group is characterized by the -CONH- linkage.
2. Apply the classification: • Option A (RCOOR) represents an ester, not an amide. • Option B (RCONH₂) shows the nitrogen bonded to two hydrogens and one R-CO group. This fits the definition of a primary amide. • Option C (RCONHR) shows the nitrogen bonded to one hydrogen and two carbon-based groups. This is a secondary amide. • Option D (RCONR₂) shows the nitrogen bonded to no hydrogens and three carbon-based groups. This is a tertiary amide.

Conclusion

Based on the structural classification of amides, the formula for a primary amide is RCONH₂.

Exam Tip: Think of the number of alkyl (R) groups attached to the nitrogen.

• Primary = 0 R groups on the Nitrogen (RCONH₂)
• Secondary = 1 R group on the Nitrogen (RCONHR)
• Tertiary = 2 R groups on the Nitrogen (RCONR₂)