Question

How could IR spectroscopy be used to distinguish between benzene and cyclohexene?

Answer 1

Hint: The answer lies in the fact that IR spectroscopy distinguishes the compounds based on the vibration of their bonds and the answer is based on the carbon hydrogen stretching.

Complete step by step answer:
In the classes of chemistry, we have studied about various types of the absorption spectrum such as IR spectra, Raman spectra, UV spectra and many more which are used for the identification of the compounds.
Let us now see in detail about the IR spectra and also how can we differentiate the compounds in this spectroscopy.
- IR spectroscopy or infrared spectroscopy which is also called as the vibrational spectroscopy is the spectroscopy which is used for studying and identification of the chemical substances or also the functional groups in the solid, liquid or the gaseous form.
- This spectroscopy distinguishes the compounds based on the vibrations of their bonds and the stretching of the $C-H$ bond.
- Cyclohexene has the aliphatic $C-H$ bonds and the absorptions of these bond stretching is observed at $3000-2850c{m}^{-1}$
- In the case of benzene, the aromatic absorptions are in the regions of $1600-1585c{m}^{-1}$ and $1250-1400c{m}^{-1}$ due to the carbon – carbon stretching vibrations in the aromatic ring.
Thus, based on this fact above, benzene and cyclohexene can be distinguished.
The key difference lies in the fact that cyclohexene has strong aliphatic $C-H$ stretching peaks at $3000-2850c{m}^{-1}$ and benzene does not have.

Note: Note that the IR spectroscopy is mainly used for the determination of the functional groups present in a given molecule and is important spectroscopy which is used for structural elucidation and compound identification.