Dear friends, Please read our latest blog post for an important announcement about the website. ❤, The Socratic Team

How does infrared spectroscopy identify functional groups?

1 Answer
Write your answer here...
Start with a one sentence answer
Then teach the underlying concepts
Don't copy without citing sources


Write a one sentence answer...



Explain in detail...


I want someone to double check my answer

Describe your changes (optional) 200


Vibrating bonds in functional groups absorb energy at a frequency that corresponds to the vibrational frequency of the bond.

In organic chemistry, this corresponds to frequencies of 15 to 120 THz.

These frequencies are expressed as wavenumbers:

#"wavenumber" = "frequency"/"speed of light" = f/c#

The wavenumbers range from 500 to 4000 cm⁻¹.

If the frequency of the radiation matches the vibrational frequency, the bond will absorb the radiation. The amplitude of the vibration will increase.

Within a narrow range, each type of bond vibrates at a characteristic wavenumber. This makes infrared spectroscopy useful for identifying functional groups in a molecule.

Here’s a short table of common absorption frequencies.

Notice how you can identify the important vibrations in the spectrum of ethyl acetate.

The video below gives a simple explanation of infrared spectroscopy.

Was this helpful? Let the contributor know!
Impact of this question
4465 views around the world
You can reuse this answer
Creative Commons License