Spectroscopy is using light to determine what kind of substance it is. While spectroscopic techniques vary wildly in nature, all have one thing in common- “They shine light be a subject and look at what's coming out of it to determine what's inside”.
Spectroscopy can used to know:
“The field of organic structure determination attempts to answer these questions”.
Instrumental methods of structure determination
1. Infrared Spectroscopy (IR) -Triggering molecular vibrations through irradiation with infrared light. Provides mostly information about the presence or absence of certain functional groups.
2. Nuclear Magnetic Resonance (NMR) – Excitation of the nucleus of atoms through radiofrequency irradiation. Provides extensive information about molecular structure and atom connectivity
3. Mass spectrometry – Bombardment of the sample with electrons and detection of resulting molecular fragments. Provides information about molecular mass and atom connectivity.
4. Ultraviolet spectroscopy (UV) – Promotion of electrons to higher energy levels through irradiation of the molecule with ultraviolet light. Provides mostly information about the presence of conjugated p systems and the presence of double and triple bonds.
Most organic spectroscopy uses electromagnetic energy, or radiation, as the physical stimulus.
Electromagnetic energy (such as visible light) has no detectable mass component. In other words, it can be referred to as “pure energy.”
Other types of radiation such as alpha rays, which consist of helium nuclei, have a detectable mass component and therefore cannot be categorized as electromagnetic energy.
The important parameters associated with electromagnetic radiation are:
Effect of electromagnetic radiation on molecules