How could IR spectroscopy be used to distinguish between the

How could IR spectroscopy be used to distinguish between the following pair of compounds? 9. i. (CH3)3N and CH3NHCH2CH3 ii. HOCH2CH2CHO and CH3CH2CO2H

Solution

i. The energy level of infrared light corresponds to the energy required to cause molecular vibrations.The energy of the infrared light can interact with the resonant vibrational frequency of the bond. Since different bonds have different energies, they require different energy to cause vibration.

NH bond is more stiff .Its presence in CH₃NHCH₂CH₃ will show presence of more vibrational energy then CN bonds present in (CH₃)₃N

ii. Depending upon what type of bond is present determines the exact energy required to cause the vibration.The energy of light absorbed therefore indicates what functional group is present.

HOCH₂CH₂CHO contains CHO aldehyde group while CH₃CH₂CO₂H contains carboxylic group.

Wawenumber for aldehyde group\'s absorption is 1700-1730cm^-1and 2700-2800cm^-1 two peaks

Wavenumber for carboxyl group\'s absorption is 3000 cm^-1

Thus IR absorption spectra can be used to distinguish pair of compounds.