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Encyclopedia > Cis isomer

In chemistry, geometric isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. Such bonds are typically double bonds, but they can also be part of a ring structure which prevents rotation. Chemistry (in Greek: χημεία) is the science of matter and its interactions with energy and itself (see physics, biology). ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ... In ecology functional groups are collections of organisms based on morphological, physiological, behavioral, biochemical, or environmental responses or on trophic criteria. ... A chemical bond is the phenomenon of atoms being held together in molecules or crystals. ...


Sometimes the term "geometric isomerism" is used as a synonym of stereoisomerism, i.e. optical isomers are considered to be geometric isomers. The exact term for stereoisomers that are not optical isomers is diastereomers. Optical isomerism is a form of isomerism (specifically stereoisomerism) whereby the different 2 isomers are the same in every way except being non-superposable mirror images1 of each other. ...


There are two forms of a geometric isomer, the cis and trans versions. The form in which the substituent groups are on the same side of the bond that doesn't allow rotation is called cis; the form in which the substituents are on opposite sides of the bond is called trans. CIS is an abbreviation of: Commonwealth of Independent States Canadian Interuniversity Sport Contact Image Sensor CompuServe Information Service Chinese International School Confederacy of Independent Systems (Star Wars) Continuous injection system Communication Information Services Card Information Structure Cisalpino See also uses of the word cis. ... Trans is a Latin word meaning 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 is called trans. ... In organic chemistry, a substituent is an atom or group of atoms subsituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ...


Cis isomers and trans isomers of a substance have different physical properties. Trans isomers generally have higher boiling points and lower densities. This is because the trans isomers molecules can line up and fit together better than the cis form. The boiling point of a substance is the temperature at which it can change state from a liquid to a gas throughout the bulk of the liquid. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ...


As an example of a geometric isomer due to a ring structure, consider 1,2-dichlorocyclohexane:

image:trnC6H10Cl2.png image:cisC6H10Cl2.png
trans-1,2-dichlorocyclohexane cis-1,2-dichlorocyclohexane

Another notation can be used for cis and trans molecules. Z from the German Zusammen, which means together can replace the term cis; and E from the German Entgegen who means in opposite of can replace the term trans. In alkene notation a distinction can be made between a Z alkene and a E alkene for instance in (Z)-1-bromo-1,2-dichloroethene which is different from the E isomer. This alternate system of designation is necessary when there are more than two different substituents on a double bond. Whether a molecular configuration is the Z or E is determined by the Cahn Ingold Prelog priority rules of the substituents. 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. An alkene is an unsaturated hydrocarbon containing at least one carbon-carbon double bond. ... 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. ...


  Results from FactBites:
 
Our Deadly Diabetes Deception (9670 words)
It is the combined absence of the CIS w=3 fats and oils and the presence of these saturated and trans-fats and other toxic isomers that cause these cellular membranes to become stiff and sticky instead of fluid and slippery.
These toxic isomers are just different geometries of the unsaturated oil molecules many of which were, before processing, of the CIS type.
When delicate CIS w=3 oils are over heated, either in cooking or refining, the oil undergoes irreversible changes; the CIS configuration is destroyed and many toxic isomers are generated, including the notorious trans-isomer.
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