Cis-2-butene

Trans-2-butene

In chemistry, geometric isomerism or cis-trans isomerism is a form of stereoisomerism and describes the orientation of functional groups within the molecule. Such isomers typically contain double bonds which cannot rotate, but they can also arise from ring structures where the rotation of bonds is greatly restricted. Image File history File links Cis-2-butene. ... Image File history File links Trans-2-butene. ... Chemistry (from Greek χημεία khemeia[1] meaning alchemy) is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms, such as molecules, crystals, and metals. ... Main article: stereochemistry Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ... In organic chemistry, functional groups are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ...

According to IUPAC the term "geometric isomerism" is an obsolete synonym of "cis-trans isomerism" and its use is strongly discouraged. Sometimes the term "geometric isomerism" has been used as a synonym of stereoisomerism, i.e. optical isomers being considered to be geometric isomers. This, however, is not consistent with current standard chemical nomenclature. The exact term for stereoisomers that are not optical isomers is diastereomers. The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ... Optical isomerism is a form of isomerism (specifically stereoisomerism) where the two different isomers are the same in every way except being non-superposable mirror images of each other. ... Optical isomerism is a form of isomerism (specifically stereoisomerism) where the two different isomers are the same in every way except being non-superposable mirror images of each other. ... Diastereomers are stereoisomers that are not enantiomers, or mirror images of each other. ...

There are two forms of a geometric isomer, the cis and trans versions. When the substituent groups are oriented in the same direction the diastereomer is referred to as cis. While when the substituents are oriented in opposing directions the diastereomer is referred to as trans. An example of a small hydrocarbon displaying cis-trans isomerism is 2-butene. CIS usually refers to: Commonwealth of Independent States, a modern-day political entity consisting of 11 former Soviet Union Republics CIS is also an acronym for: Canadian Interuniversity Sport Cancer Information Service Carcinoma in situ Centre for Independent Studies Center for Immigration Studies Chinese International School Cisalpino Citizenship & Immigration Services... Trans is a Latin word meaning across, beyond or on the opposite side and is the opposite of cis, which means on the same side. In chemistry, a bond not subject to free rotation in which the greater radical on both ends is on the opposite side of the bond... In organic chemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ... 1-butene cis-2-butene trans-2-butene methylpropene There are four isomers of alkenes which have the chemical formula C4H8. ...

Alicyclic compounds can also display cis-trans isomerism. As an example of a geometric isomer due to a ring structure, consider 1,2-dichlorocyclohexane: Cyclopropane is the smallest alicyclic compound. ...

trans-1,2-dichlorocyclohexane	cis-1,2-dichlorocyclohexane

Image File history File links trans-isomer of 1,2-dichlorocyclohexane File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links cis-isomer of 1,2-dichlorocyclohexane File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

Cis vs trans physical properties

Cis isomers and trans isomers often have different physical properties. Differences between isomers generally arise from the differences in the shape of the molecule or the overall dipole moment. These differences can be very small as in the case of the boiling point of straight chained alkenes, such as 2-pentene where the trans isomer has a boiling point of 36°C and cis isomer is 37°C ^[1]. The differences between cis and trans isomers can also be quite large as in the case of cyclooctene. The cis isomer in this case has a boiling point of 145°C ^[2], while the trans isomer has a boiling point of 75°C ^[3]. The large difference between the two isomers of cyclooctene arise from the large ring strain for trans-cyclooctene, which also makes it significantly less stable than the cis isomer. In fact the two isomers of 2-butenedioic acid have such large differences in properties and reactivities that they were actually given completely different names. The cis isomer is called maleic acid and the trans is named fumaric acid. This article is about the electromagnetic phenomenon. ... Maleic acid or (Z)-Butenedioic acid or cis-butenedioic acid or malenic acid or maleinic acid or toxilic acid is an organic compound which is a dicarboxylic acid (molecule with two carboxyl groups). ... Fumaric acid (IUPAC systematic name: 2-butenedioic acid), also called allomaleic acid, boletic acid or lichenic acid, is a colorless crystalline flammable carboxylic acid based on butene and molecular formula C4H4O4. ...

In the case of geometric isomers that are a consequence of double bonds and in particular when both substituents are the same some general trends usually hold. These trends can be attributed to the fact that the dipoles of the substituents will add when together for a cis isomer to give an overall molecular dipole while for trans isomer the dipoles of the substituents will cancel out ^{[citation needed]}. Trans isomers also tend to have lower densities than their cis counterparts.^{[citation needed]}

March ^[4] observes that as trans alkenes in general have more symmetry that cis alkenes, the trans alkenes also tend to have higher melting points and lower solubility in inert solvents. The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... It has been suggested that Solid solubility be merged into this article or section. ...

Stability

According to March trans isomers also have a lower heat of combustion, indicating higher thermochemical stability. In the Benson Heat of formation group additivity dataset cis isomers suffer a 1.10 kcal/mol stability penalty. Exceptions to this rule exist. For instance for 1,2-difluoroethylene, 1,2-difluorodiazene (FN=NF) and several other halogen and oxygen substituted ethylenes the cis isomer is more stable than the trans isomer ^[5]. This phenomenon is called the cis effect ^[6]. The Heat of combustion (ΔcH0) is the energy released as heat when a compound undergoes complete combustion with oxygen. ... In the thermodynamics and physical chemistry, thermochemistry is the study of the heat evolved or absorbed in chemical reactions. ... Heat of formation group additivity methods in thermochemistry enable the calculation and prediction of heat of formation of organic compounds based on additivity. ...

E/Z notation

The trans/cis system for naming isomers breaks down when there are more than two different substituents on a double bond. The E/Z notation should then be used. Z (from the German zusammen) means together and corresponds to the term cis; E (from the German entgegen) means opposite and corresponds to the term trans.

Whether a molecular configuration is designated E or Z is determined by the Cahn Ingold Prelog priority rules. For each of the two atoms in the double bond, individually determine which of the two substituents is of a higher priority. If both of the substituents of higher priority are on the same side, the arrangement is Z; if they are on opposite sides the arrangement is E. For compounds found in organic chemistry, the Cahn Ingold Prelog priority rules are used to determine the orientation of a molecule for purposes of assigning stereochemistry at a stereocenter and for assigning the name of isomers of molecules possessing double bonds such as alkenes. ...

An example of a compound named in this manner is (Z)-1-bromo-1,2-dichloroethene.

External links

• The IUPAC definition of "stereoisomerism"
• The IUPAC definition of "geometric isomerism"
• The IUPAC definition of "cis-trans isomers"

See also

• Important publications in organic chemistry

This is a list of important publications in chemistry, organized by field. ...

References

1. ^ Chemicalland values
2. ^ Akros data
3. ^ Organic Syntheses, Coll. Vol. 5, p.315 (1973); Vol. 49, p.39 (1969) Link
4. ^ Advanced organic Chemistry, Reactions, mechanisms and structure 3ed. page 111 Jerry March ISBN 0-471-85472-7
5. ^ The stereochemical consequences of electron delocalization in extended .pi. systems. An interpretation of the cis effect exhibited by 1,2-disubstituted ethylenes and related phenomena Richard C. Bingham J. Am. Chem. Soc.; 1976; 98(2); 535-540 Abstract
6. ^ Contribution to the Study of the Gauche Effect. The Complete Structure of the Anti Rotamer of 1,2-Difluoroethane Norman C. Craig et al. J. Am. Chem. Soc.; 1997; 119 p 4789 DOI:10.1021/ja963819e