Recently, a colleague asked me about the possibility of distinguishing 2-pentanone and 2-hexanone with absolute structural information.

I am happy to report that this is possible! In fact, if you can measure these two molecules in an infrared spectroscopy experiment .

Which is relatively simple to do – then it’s straightforward to distinguish them using their IR spectra alone.

This blog post will explain how it works!

How IR Spectroscopy Works IR spectroscopy relies on the measurement of how molecules absorb light in a particular frequency range.

By measuring which frequencies are absorbed and which aren’t, we can gain information about what types of bonds exist between different groups within the molecule (e.g., C=O).

For example, if two adjacent carbon atoms have an “open bond” where they share electrons with each other, this will allow them to more easily take up energy from infrared radiation at higher energies – around 300 cm-¹ .

Because their electron orbitals overlap better than those that don’t share a bond.

Conversely, it’s hard for such open bonds to absorb lower energy photons like ultraviolet or visible.


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