With the help of quantum mechanical calculations (Schroedinger equation) you can find the frequencies of basic stretching and bending modes: Based on the equation, one would always expect a sharp lines at a well defined wavenumber.
Unfortunately, the change in vibration modes is always accompanied with change in rotational mode (Stokes and Anti-Stokes).
The O-H-stretching modes from alcohols and phenols (example 5) are mostly broad and very strong (3200-3650 cm The change in peak shape is a result of the different degree of hydrogen bonds in alcohol and carboxylic acids.
These peaks change significantly with the polarity of the solvent.
However, if there is a carbonyl group present, it might be difficult to locate a weak or medium sized peak right next to it. If there is a coupling between a C=C-group and other double bonded systems e.g.
C=O or aromatic systems, the intensity will increase due to the increase in dipole momentum in the double bond.
In some cases you can find information about the substitution pattern of alkenes or aromatic ring systems, if the range between 700-900 cm Nobody is expected to memorize all those numbers.
A lot of details can be deducted if a basic understanding of general trends is there.
A medium or strong peak in this area corresponds to aromatic ring.
A nitro group shows two very intense peaks in the range between 1300-1400 cm (out of plane modes, C-X: X=Cl, Br, I, heavier atoms) This range belongs to the fingerprint area, where assignments are a little bit uncertain.