Saturated and unsaturated compounds

A saturated compound is a chemical compound (or ion) that resists addition reactions, such as hydrogenation, oxidative addition, and binding of a Lewis base. The term is used in many contexts and for many classes of chemical compounds. Overall, saturated compounds are less reactive than unsaturated compounds. Saturation is derived from the Latin word saturare, meaning 'to fill'.[1]

This article is about chemical bonds. For saturation status of solutions, see solubility and supersaturation.

Organic chemistry

Generally distinct types of unsaturated organic compounds are recognized. For hydrocarbons:

  • alkene (unsaturated) vs alkane (saturated)
  • alkyne (unsaturated) vs alkane (saturated)
  • arene (unsaturated) vs cycloalkane (saturated)

For organic compounds containing heteroatoms (other than C and H), the list of unsaturated groups is long but some common types are:

Saturated compounds

Ethane

Propane

1-Octanol

Unsaturated compounds

Ethylene

Acetylene

alpha-Linolenic acid, an unsaturated fatty acid

Unsaturated compounds generally carry out typical addition reactions that are not possible with saturated compounds such as alkanes. A saturated organic compound has only single bonds between carbon atoms. An important class of saturated compounds are the alkanes. Many saturated compounds have functional groups, e.g., alcohols.

Unsaturated organic compounds

The concept of saturation can be described using various naming systems, formulas, and analytical tests. For instance, IUPAC nomenclature is a system of naming conventions used to describe the type and location of unsaturation within organic compounds. The "degree of unsaturation" is a formula used to summarize and diagram the amount of hydrogen that a compound can bind. Unsaturation can be determined by NMR, mass spectrometry, and IR spectroscopy, or by determining a compound's bromine number or iodine number.[2]

Fatty acids and fats
Main article: Unsaturated fat
Further information: Hydrogenation ยง Food industry

The terms saturated vs unsaturated are often applied to the fatty acid constituents of fats. The triglycerides (fats) that comprise tallow are derived from the saturated stearic and monounsaturated oleic acids.[3] Many vegetable oils contain fatty acids with one (monounsaturated) or more (polyunsaturated) double bonds in them.

Saturated and unsaturated compounds beyond organic chemistry

Organometallic chemistry

In organometallic chemistry, a coordinatively unsaturated complex has fewer than 18 valence electrons and thus is susceptible to oxidative addition or coordination of an additional ligand. Unsaturation is characteristic of many catalysts. The opposite of coordinatively unsaturated is coordinatively saturated. Complexes that are coordinatively saturated rarely exhibit catalytic properties.[4][5]

Surfaces
Further information: Surface science

In physical chemistry, when referring to surface processes, saturation denotes the degree at which a binding site is fully occupied. For example, base saturation refers to the fraction of exchangeable cations that are base cations.

References
  1. Mosby's Medical, Nursing & Allied Health Dictionary, Fourth Edition, Mosby-Year Book Inc., 1994, p. 1394
  2. Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 978-0-471-72091-1
  3. Alfred Thomas (2002). "Fats and Fatty Oils". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a10_173. ISBN 3527306730.
  4. Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. ISBN 1-891389-53-X
  5. "IUPAC definition of Coordinatively Unsaturated Complex". doi:10.1351/goldbook.C01334.
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