File Name: e and z configuration .zip
Illustrated Glossary of Organic Chemistry. Relative configuration : The position of atoms or groups in space in relation to i. Compare with absolute configuration , which is independent of atoms or groups elsewhere in the molecule. Relative to the position of the methyl group , the chlorine atom is on the same face of the cyclohexane ring. The stereocenter bearing the chlorine atom has an R absolute configuration this configuration does not involve or depend on positions elsewhere in the molecule.
7.7: Sequence Rules - The E,Z Designation
AdiChemistry Home. The isomerism which arises due to different spatial arrangements of atoms or groups is called stereo isomerism. It is broadly divided into:. The stereo isomers have same structural formula i. However the atoms or groups are arranged differently in space. The geometrical isomerism arises when atoms or groups are arranged differently in space due to restricted rotation of a bond or bonds in a molecule. In the cis isomer, the two methyl groups are arranged on the same side of a double bond.
Part A few details of differences in physical and chemical properties are pointed out where it seems appropriate. Cis and trans notation is still to be found in older textbooks and even some contemporary literature. Sub-index for this page. There are two main sub-divisions of stereoisomerism:.
In the previous post, we talked about the cis and trans designation of alkenes. The cis and trans approach works only if two identical groups are connected to the double bond. We cannot classify these as cis or trans because none of the two groups on the double bond are identical. However, there should be a way of distinguishing them since they are not identical. So, how is the E and Z configuration of a double bond determined? Here is the principle; you need to look at each carbon of the double bond separately. And the goal is to first determine which of the two groups on each carbon has a higher priority.
At first you might say cis, because it appears that two ethyl groups appear on the same side of the double bond. However, the correct answer is trans. The rule is that the designation cis or trans must correspond to the configuration of the longest carbon chain. Tracing out the seven-carbon chain in the compound shown above, you change sides as you pass through the double bond:. In cases where two or more double bonds are present, you must be prepared to assign an E or Z designation to each of the double bonds. For example:.
These two molecules have different physical properties — different boiling points, melting points, reactivities, spectral characteristics and so on. We apply this to two stereoisomers which are non-superimposable mirror images of each other. They also have at least one substituent in common H. This stands in contrast to conventional sigma bonds single bonds in acyclic molecules, where free rotation is possible: witness 1,2-dichloroethane below left.
If you have come straight here via a search engine, you should be aware that this page follows on from an introductory page about geometric isomerism. Unless you are already confident about how geometric isomers arise, and the cis-trans system for naming them, you should follow this link first. You will find links back to this current page at suitable points on that page. Consider a simple case of geometric isomerism which we've already discussed on the previous page. You can tell which is the cis and which the trans form just by looking at them.