Chemistry

Worked example 3

The compound C₇H₈O has infrared absorption bands over the range: 690–740, 1450–1490, 1700–2000 and 3310 cm⁻¹. Based on correlation tables, what are the probable structures for this compound?

First calculate the IHD – reference hydrocarbon is C₇H₁₆

so IHD = (16 − 8)/2 = 4. The compound contains a benzene ring.

From correlation tables:

Absorption 690–740 cm⁻¹ corresponds to aromatic C–H

Absorption 1450–1490 cm⁻¹ corresponds to a benzene ring

Absorption 1700–2000 cm⁻¹ corresponds to a benzene ring

Absorption 3310 cm⁻¹ corresponds to –OH functional group.

1. 4 structures are possible:
2. 
3. 
4. 
5. 

(Note: It is difficult to differentiate between these structures based on IR data alone.)