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The system most often studied for the cis effect is an octahedral complex M(CO) 5 X where X is the ligand that will labilize a CO ligand cis to it. Unlike the trans effect, which is most often observed in 4-coordinate square planar complexes, the cis effect is observed in 6-coordinate octahedral transition metal complexes.
2 are cis, if the L b ligands are mutually adjacent, and trans, if the L b groups are situated 180° to each other. It was the analysis of such complexes that led Alfred Werner to the 1913 Nobel Prize–winning postulation of octahedral complexes.
The analogous cis effect is most often observed in octahedral transition metal complexes. In addition to this kinetic trans effect, trans ligands also have an influence on the ground state of the molecule, the most notable ones being bond lengths and stability. Some authors prefer the term trans influence to distinguish it from the kinetic ...
Cis and trans isomers occur both in organic molecules and in inorganic coordination complexes. Cis and trans descriptors are not used for cases of conformational isomerism where the two geometric forms easily interconvert, such as most open-chain single-bonded structures; instead, the terms "syn" and "anti" are used.
The descriptors cis (Latin, on this side of) [2] and trans (Latin, over, beyond) [3] are used in various contexts for the description of chemical configurations: [4] [5] In organic structural chemistry , the configuration of a double bond can be described with cis and trans , in case it has a simple substitution pattern with only two residues.
Traditionally, double bond stereochemistry was described as either cis (Latin, on this side) or trans (Latin, across), in reference to the relative position of substituents on either side of a double bond. A simple example of cis–trans isomerism is the 1,2-disubstituted ethenes, like the dichloroethene (C 2 H 2 Cl 2) isomers shown below. [7]
This arrangement is illustrated by complexes of the Trost ligand. The ligand can bend so that one donor atom is at the pole and the remaining three are on the equator of the central atom. This is called cis-β (beta). The remaining octahedral positions are cis (adjacent) to each other. The triangles of coordinating atoms and the central atom ...
For a nondissociative pathway, reductive elimination occurs from the four-coordinate system to afford a two-coordinate complex. If the eliminating ligands are trans to each other, the complex must first undergo a trans to cis isomerization before eliminating. In an associative mechanism, a ligand must initially associate with the four ...