7.2.2 What Kind of Isomer

We have just introduced four different types of isomers, which fall into two main classes. Structural isomers include linkage isomers and coordination isomers. Stereoisomers include geometric isomers and optical isomers. Structural isomers are compounds with identical molecular formulas, but different connections between the atoms. Stereoisomers are compounds with identical molecular formulas and identical connections between the atoms, but different arrangements of the atoms in space.

Linkage isomers are compounds that differ in the atom of a ligand that binds to a metal ion in a coordinate covalent bond. Coordination isomers, on the other hand, are compounds that differ only in the way the ligands and the counter-ions are distributed around the central ion. This seems confusing. Have you come up with a way to keep from confusing linkage isomers and coordination isomers?

Geometric isomers are compounds that differ only in the relative positions of some atoms. For example, trans-2-butene and cis-2-butene differ only in the positions of the CH3 groups relative to the double bond. Optical isomers differ only in the way they rotate plane-polarized light. These pairs of molecules are called chiral. Once again, the distinction between geometric isomes aand optical isomers seems confusing. Have you thought of a way to keep geometirc isomers and optical isomers straight?

In this discussion, first compare notes on the different types of isomers we have covered to make sure that everyone agrees on the different classes of isomers. Use an example if possible to help explain your answer. Then tell your classmates the ways that you have developed to determine what ype of isomer a pair of compounds represents. Also, use this as an opportunity to discuss what you find most confusing about isomers and see if your classmates have suggestions about making isomers more understandable.