Question

How could IR spectroscopy distinguish between $ \text{1hexyne, 2hexyne, 3hexyne} $ .

Answer 1

Hint :We know that 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. Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms.
Let us now see in detail about the IR spectra and also how we can 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 identifications 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.
The given absorption can be attributed to the stretching of the $ C\equiv C-H~ $ bond (i.e. the $ C-H $ part of the bond gives rise to the absorption). In principle, this could be used to identify the terminal alkyne from $ \text{2hexyne, 3hexyne} $ . In fact, the only way would be to substitute the terminal hydrogen with deuterium, and see if a new absorption appears at lower frequency.
IR spectroscopy detects the absorption of light by a compound, in the IR region of the electromagnetic spectrum. To absorb light a molecule must have a bond within its structure that can exhibit what is referred to as a 'dipole moment' which means electrons within a bond are not shared equally.

Note :
Note that the infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms.