Stereochemistry and Isomers

Figure 29.

STEREOCHEMISTRY AND ISOMERS

In describing isomers of different types of organic molecules, you need to know that there are different types of isomers. Isomers, by definition, have different shapes and arrangements but the same number of atoms per molecule. The one thing that isn’t an isomer is when a molecule rotates on an axis. This happens all the time with organic molecules but doesn’t necessarily represent a different molecule. Molecules can be long and unwieldy but aren’t actually different if they are in different rotational shapes.

Structural isomers have completely different orders of molecules. The most obvious is the “chain” isomer. This involves different types of branching in the molecule. For example, C4H10 can be a single chain of carbon atoms to make butane. It can also involve a single carbon atom with a hydrogen on one side and three methyl (CH3) side chains on the other 3 sides.

Position isomers have the basic carbon skeleton left unchanged; however, important groups are moved around on the skeleton. An example is C3H7Br. This is propane with a bromine atom attached. The bromine atom can be attached to the end, making it 1bromopropane. It can also be attached to the middle of the chain, making it 2bromopropane. The carbon atoms are still in the same position but the bromine has shifted around. The same thing happens with an alcohol of a chain. The chain stays the