Question

If the force constant is approximately the same for `C-C`, `C-N`, and `C-O` bonds, how can I predict the relative positions of their stretching vibrations in an IR spectrum?

Answer 1

You can't.

Explanation:

The `"C-C"`, `"C-N"`, and `"C-O"` groups all appear in the region from `1300` to `"1000 cm"^-1`.

The region from about `1500` to `"500 cm"^-1` is called the fingerprint region.

It usually contains a complicated series of absorptions that are caused by many different vibrations within the molecule.

This region is often useful only for confirming the presence of functional groups that you have identified in other areas of the spectrum.

(from www.mhhe.com)

For example, the spectrum above shows that there is probably an `"OH"` group, so one of the strong bands between `1200` and `"1100 cm"^-1` is probably a `"C-O"` stretching vibration.