A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as diatomic oxygen or nitrogen molecules, to the very complex, such as protein or DNA molecules. Molecular geometry can be roughly represented using a structural formula. Electronic structure describes the occupation of a molecule's molecular orbitals.
The theory of chemical structure was first developed by Aleksandr Butlerov, which stated that the chemical compounds are not a random cluster of atoms and functional groups but structures with definite order formed according the valency of the composing atoms. Other important contributors were Archibald Scott Couper and Friedrich August Kekule.
Structural determination in chemistry is the process of determining the chemical structure of molecules. Practically, the end result of such process is the obtainment of the coordinates of the atoms in a molecule. The methods by which one can determine the structure of a molecule include spectroscopy, such as nuclear magnetic resonance (NMR), infrared spectroscopy and Raman spectroscopy, electron microscopy, and x-ray crystallography (x-ray diffraction). The last technique can produce three-dimensional models at atomic-scale resolution, as long as crystals are available, as x-ray diffraction needs numerous copies of the molecule being studied that must also be arranged in an organised way.
The following are common methods for determining the chemical structure (Structural elucidation) :
The following are common methods for determining the electronic structure:
- Electron-spin resonance
- Cyclic voltammetry
- Electron absorption spectroscopy
- X-ray photoelectron spectroscopy
- Pauli exclusion principle
- Lipinski's Rule of Five, describing molecular properties of drugs
- QSAR, quantitative structure–affinity relationship
- Chemical property
- Molecular property
- Physical property
- Crystallographic database