Spectroscopy in organic chemistry can be divided into two main types: qualitative and quantitative. Each type has its own special purpose.

Qualitative Spectroscopy:

• This type is all about figuring out what is in a sample.
• It uses techniques like IR (Infrared) and NMR (Nuclear Magnetic Resonance) spectroscopy.
• For example, IR spectroscopy can help find specific groups of atoms in a molecule, such as carbonyl groups.

Quantitative Spectroscopy:

• This type measures how much of a substance is in a sample.
• One common technique is UV-Vis (Ultraviolet-Visible) spectroscopy.
• An example of this is how UV-Vis can find out the concentration of color in a solution using Beer’s Law, which is written as $A = \varepsilon c l$. Here, $A$ stands for absorbance, $\varepsilon$ is a constant that describes how well the substance absorbs light (molar absorptivity), $c$ is the concentration of the substance, and $l$ is the path length that the light travels through the solution.

Knowing the difference between these two types of spectroscopy helps scientists choose the best method for identifying and analyzing chemical compounds.