User:Cns1008/Cahn–Ingold–Prelog priority rules

Isotopes
According to James Ashenhurst, isotopes receive their priority designation based on their atomic mass.

''For this edit I would not include "According to James Ashenhurst". The citation does that for you. I might just keep the original text and add the citation. -R''

Double bonds: E/Z
Main article: E-Z notation

(R edited the entire original thing...)For double bonded molecules, Cahn–Ingold–Prelog priority rules (CIP rules) are followed to determine the priority of substituents of the double bond. If both of the high priority groups are on the same side of the double bond (cis configuration), then the stereoisomer is assigned the configuration Z (zusammen, German word meaning "together"). If the high priority groups are on opposite sides of the double bond ( trans configuration ), then the stereoisomer is assigned the configuration E (entgegen, German word meaning "opposed")

Double and triple bonds
If an atom, A, is double-bonded to another atom, then atom A should be treated as though it is "connected to the same atom twice". An atom that is double-bonded has a higher priority than an atom that is single bonded.

When B is replaced with a list of attached atoms, A itself, but not its "phantom", is excluded in accordance with the general principle of not doubling back along a bond that has just been followed. A triple bond is handled the same way except that A and B are each connected to two phantom atoms of the other.

Stereocenters: R/S
Add (Mikayla): In a normal configurational isomer, the lowest priority group (hydrogen) is positioned behind the plane or the hatched bond going away from you. The highest priority group, the group with the highest atomic mass, will have an arc drawn connecting to the rest of the groups, finishing at the group of third priority. An arc drawn clockwise, has the rectus (R) assignment. An arc drawn counterclockwise, has the sinister (S) assignment. When naming an organic isomer, the abbreviation for either rectus or sinister assignment is placed in front of the name in parentheses. For example, 3-methyl-1-pentene with a rectus assignment is formatted as (R) 3-methyl-1-pentene. When dealing with double bonded priority groups, you are allowed to visit the same atom twice.

Optical Isomerism
Optical isomers are compounds that have four different substituents attached to a central carbon. Optical isomers play a significant role in biological activity. Optical isomers have the ability to rotate plane-polarized clockwise (R) or counterclockwise (S). When optical isomers create two enantiomers, one will rotate clockwise while the other rotates counterclockwise. A mixture of the two isomers, however, will not rotate plane-polarized. These two isomers may be identical chemically, but are indistinguishable.

Spiro Compounds
Spiro structures contain chiral molecules with no say asymmetric center. The rings of a spiro structure lie at right angles to each other. It's important to note that the mirror images of spiro structures are non-superimposable and are enantiomers.

A molecule is classified as chiral if it is asymmetric or if there is only one axis of symmetry.

Diastereomers
Diastereomers do not obtain mirror images of one another, nor does it have the same chemical and physical effects.

Geometric Isomers
A stereoisomer that contains two higher priority groups on the same face of the double bond (cis) is classified as "Z." The stereoisomer with two higher priority groups on opposite sides of a carbon-carbon double bond (trans) is classified as "E."

Describing Multiple Centers
When the numerical assignment of stereocenters is not unique because of mirror symmetry of the entire molecule, the result is a meso compound such as meso-tartaric acid, in which (R,S) is the same as the (S,R) form. In meso compounds the R and S stereocenters occur in symmetrically positioned pairs.

(R editing into...) A meso compound is an achiral molecule, despite having two or more stereogenic centers. A meso compound is "superimposable" on its mirror image, therefore it reduces the number of stereoisomers predicted by the 2n rule. One example is meso-tartaric acid, in which (R,S) is the same as the (S,R) form. In meso compounds the R and S stereocenters occur in symmetrically positioned pairs.

Coordination Compounds
In some cases where stereogenic centers are formed, the configuration must be specified. Without the presence of a non-covalent interaction, a compound is achiral. Some professionals have proposed a new rule to account for this. This rule states that "non-covalent interactions have a fictitious number between 0 and 1" when assigning priority. Compounds in which this occurs are referred to as coordination compounds.