**Differentiating between o-hydroxy benzaldehyde and p-hydroxy benzaldehyde by IR spectroscopy**

**Introduction**

IR spectroscopy is a powerful analytical technique that is commonly used to identify and differentiate between different compounds based on their functional groups. In the case of o-hydroxy benzaldehyde and p-hydroxy benzaldehyde, IR spectroscopy can be employed to distinguish between these two isomers based on the position of the hydroxy group on the benzene ring.

**IR Spectroscopy Principle**

IR spectroscopy measures the absorption of infrared radiation by a molecule, which causes molecular vibrations. Different functional groups have characteristic vibrational frequencies, allowing for the identification of the functional groups present in a compound.

**o-Hydroxy Benzaldehyde**

o-Hydroxy benzaldehyde, also known as ortho-hydroxy benzaldehyde, has the hydroxy group in the ortho position on the benzene ring. This position is denoted by the number 1 in the IUPAC nomenclature. The hydroxy group in o-hydroxy benzaldehyde is attached to the carbon atom directly adjacent to the aldehyde functional group.

**p-Hydroxy Benzaldehyde**

p-Hydroxy benzaldehyde, also known as para-hydroxy benzaldehyde, has the hydroxy group in the para position on the benzene ring. This position is denoted by the number 4 in the IUPAC nomenclature. The hydroxy group in p-hydroxy benzaldehyde is attached to the carbon atom opposite to the aldehyde functional group.

**Differentiation by IR Spectroscopy**

IR spectra of o-hydroxy benzaldehyde and p-hydroxy benzaldehyde will exhibit distinct differences that allow for differentiation between the two isomers. The key spectral features to consider are:

1. **Hydroxyl (OH) Stretching Vibration**: The hydroxyl stretching vibration occurs in the range of approximately 3200-3600 cm^-1. In o-hydroxy benzaldehyde, the hydroxyl group is in the ortho position, leading to a higher frequency of the OH stretching vibration compared to p-hydroxy benzaldehyde.

2. **Aldehyde (C=O) Stretching Vibration**: The aldehyde stretching vibration occurs in the range of approximately 1650-1750 cm^-1. Both o-hydroxy benzaldehyde and p-hydroxy benzaldehyde will exhibit this absorption peak at a similar position since the aldehyde functional group is present in both isomers.

3. **Benzene Ring Stretching Vibration**: The benzene ring stretching vibration occurs in the range of approximately 1600-1500 cm^-1. This absorption peak will be observed in both isomers, indicating the presence of the benzene ring.

4. **Ortho and Para Substituent Effects**: The position of the hydroxy group on the benzene ring affects the overall electronic environment of the molecule. This can lead to subtle differences in the intensities or positions of other absorption peaks in the IR spectra of o-hydroxy benzaldehyde and p-hydroxy benzaldehyde. However, these differences may not be significant enough to conclusively differentiate between the two isomers using IR spectroscopy alone.

**Conclusion**

In conclusion, differentiating between o-hydroxy benzaldehyde and p-hydroxy benzaldehyde can