Question

which of the structures have a major peak between 1700 and 3000 cm⁻¹? (select all that apply).

Explanation:

Step1: Recall IR - absorption ranges

The carbon - oxygen double - bond ($C=O$) in acyl chlorides absorbs around 1750 cm⁻¹. The hydroxyl group ($-OH$) in phenols has a broad absorption peak in the range of 3200 - 3600 cm⁻¹. Nitro groups ($-NO_2$) have absorption peaks around 1500 - 1600 cm⁻¹ and 1300 - 1400 cm⁻¹.

Step2: Analyze each structure

The first structure is an acyl chloride ($R - COCl$). It has a $C = O$ bond, so it will have a major peak around 1750 cm⁻¹ which is in the 1700 - 3000 cm⁻¹ range. The second structure is a phenol ($Ar - OH$). Its $-OH$ group absorption is above 3000 cm⁻¹. The fourth structure is a nitro - substituted cyclohexane. Its nitro - group absorptions are below 1700 cm⁻¹.

Answer:

The first structure (acyl chloride)