What IR peaks are present in 3-nitroacetophenone?
The Correct Answer and Explanation is:
Answer:
The infrared (IR) spectrum of 3-nitroacetophenone shows the following characteristic absorption peaks:
- C=O (carbonyl stretch): Around 1680–1700 cm⁻¹
- NO₂ group asymmetric stretch: Around 1520–1550 cm⁻¹
- NO₂ group symmetric stretch: Around 1340–1370 cm⁻¹
- Aromatic C=C stretches: Around 1450–1600 cm⁻¹
- Aromatic C–H stretching: Around 3000–3100 cm⁻¹
- C–H bending (methyl): Around 1375 cm⁻¹ and 1450 cm⁻¹
- C–C stretching (aromatic ring): Around 1100–1300 cm⁻¹
Explanation
Infrared (IR) spectroscopy is used to identify functional groups in molecules based on their vibrational transitions. In the case of 3-nitroacetophenone, the structure consists of a benzene ring substituted with a nitro group (–NO₂) at the meta position and an acetyl group (–COCH₃) at the para position relative to hydrogen.
One of the most prominent peaks is from the carbonyl (C=O) stretching of the acetyl group, typically appearing sharply between 1680 and 1700 cm⁻¹. This peak is strong due to the highly polar nature of the C=O bond.
The nitro group contributes two distinctive peaks:
- The asymmetric stretch occurs around 1520–1550 cm⁻¹
- The symmetric stretch is observed near 1340–1370 cm⁻¹
These are useful markers for identifying nitro-substituted aromatic compounds.
The aromatic ring shows C=C stretching vibrations in the region of 1450–1600 cm⁻¹. These peaks vary slightly in position and intensity depending on the substitution pattern on the ring.
The C–H stretches of aromatic hydrogens appear above 3000 cm⁻¹, typically between 3000 and 3100 cm⁻¹. In contrast, the methyl (–CH₃) group from the acetyl moiety shows C–H bending around 1375 and 1450 cm⁻¹.
Finally, there may be some fingerprint region bands below 1300 cm⁻¹ due to C–C and C–H bending modes, especially from the substituted aromatic ring, contributing to a complex pattern in the IR spectrum.
Together, these peaks confirm the presence of ketone, nitro, aromatic, and methyl groups in 3-nitroacetophenone.
