Editing Organic chemistry (section)

== Characterization ==
Since organic compounds often exist as [[mixture]]s, a variety of techniques have also been developed to assess purity; [[chromatography]] techniques are especially important for this application, and include [[High-performance liquid chromatography|HPLC]] and [[gas chromatography]].  Traditional methods of separation include [[distillation]], [[crystallization]], [[evaporation]], [[magnetic separation]] and [[solvent extraction]].

Organic compounds were traditionally characterized by a variety of chemical tests, called "wet methods", but such tests have been largely displaced by spectroscopic or other computer-intensive methods of analysis.<ref>Shriner, R.L.; Hermann, C.K.F.; Morrill, T.C.; Curtin, D.Y. and Fuson, R.C. (1997) ''The Systematic Identification of Organic Compounds''. John Wiley & Sons, {{ISBN|0-471-59748-1}}</ref>  Listed in approximate order of utility, the chief analytical methods are:
* [[Nuclear magnetic resonance|Nuclear magnetic resonance (NMR) spectroscopy]] is the most commonly used technique, often permitting the complete assignment of atom connectivity and even stereochemistry using [[correlation spectroscopy]].  The principal constituent atoms of organic chemistry – hydrogen and carbon – exist naturally with NMR-responsive isotopes, respectively <sup>1</sup>H and <sup>13</sup>C.
* [[Elemental analysis]]: A destructive method used to determine the elemental composition of a molecule.  See also mass spectrometry, below.
* [[Mass spectrometry]] indicates the [[molecular weight]] of a compound and, from the [[mass spectrum analysis|fragmentation patterns]], its structure.  High-resolution mass spectrometry can usually identify the exact formula of a compound and is used in place of elemental analysis.  In former times, mass spectrometry was restricted to neutral molecules exhibiting some volatility, but advanced ionization techniques allow one to obtain the "mass spec" of virtually any organic compound.
* [[Crystallography]] can be useful for determining [[molecular geometry]] when a single crystal of the material is available.  Highly efficient hardware and software allows a structure to be determined within hours of obtaining a suitable crystal.

Traditional spectroscopic methods such as [[infrared spectroscopy]], [[optical rotation]], and [[UV/VIS spectroscopy]] provide relatively nonspecific structural information but remain in use for specific applications. Refractive index and density can also be important for substance identification.