Are They Isomers?

How does one determine whether or not two compounds are isomers?

In order to be isomers, the two compounds must:

1. contain the same number and kinds of atoms, and
2. be non-superimposable.

 These two structures contain the same number and kinds of atoms (one each of green, yellow, purple, brown and pink), and the atoms appear to be arranged differently in space. If we select one structure and rotate, twist and/or turn it, we CAN find an orientation in which all of the atoms match up with the other structure. The two structures ARE therefore superimposable (if we were able to pick one structure up and place it on top of the other, it would be identical). Because these two structures are superimposable, they are NOT isomers.

 These two structures contain the same number and kinds of atoms (one each of yellow, red, blue, white and gray), and the atoms appear to be arranged differently in space. If we select one structure and rotate, twist and/or turn it, we CANNOT find an orientation in which all of the atoms match up with the other structure. The two structures are therefore non-superimposable (if we were able to pick one structure up and place it on top of the other, we would not be able to find an orientation in which the two structures were identical). Because these two structures are non-superimposable, they ARE isomers.