I need help with this organic chemistry problem:

 

"Organic compounds typically absorb infrared radiation. This absorption is due to: "

 

I know that an organic compound is one that contains carbon and carbon normally tends to form four single bonds with [math]sp^{3}[/math], tetrahedral geometry. Although carbon does also form double bonds resulting in either sp or [math]sp^{2}[/math] with either linear or triangular planar geometries respectively.

 

But, I do not understand how the molecular structure affects the absorption of radiation.

Molecular bonds have vibrational and rotational states, transitions of which are generally of much lower energy than atomic absorption energies. Which means they tend to absorb below the visible, which includes the IR. (vibrational tend to the IR, rotational to the RF)

 

http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/rotrig.html