Question 20.8: Identifying cis and trans Isomers Consider the following iso......
Identifying cis and trans Isomers
Consider the following isomers of the [Co(NH_3)_4(H_2O)Cl]^{2+} ion:
(a) Label the isomers as cis or trans.
(b) Which isomers are identical, and which are different?
STRATEGY
Look at the location of the H_2O and Cl^- ligands. Isomers that have H_2O and Cl^- on adjacent corners of the octahedron are cis, whereas those that have H_2O and Cl^- on opposite corners are trans. Because only two isomers are possible for complexes of the type MA_4BC, all the cis isomers are identical and all the trans isomers are identical.
(a) Isomers (1) and (4) have H_2O and Cl^- on opposite corners of the octahedron and are therefore trans isomers. Isomers (2) and (3) have H_2O and Cl^- on adjacent corners of the octahedron and are therefore cis isomers. (b) Isomers (1) and (4) are identical, as can be seen by rotating (1) counterclockwise by 90° about the vertical (z) axis:
Isomers (2) and (3) differ from (1) and (4) and are identical, as can be seen by rotating (2) clockwise by 90° about the x axis and then counterclockwise by 90° about the y axis:
