Why do the compounds hexane, hexanol, and hexene have such similar names?

Because these have the same number of carbon atoms in the structure

Explanation:

In organic chemistry, we give the name to the structure in depends on the primary chain.

In this case, the three molecules have the same number of carbon atoms, but the three have differents functional grupos.

The firts, hexane, has an alkane group (a single bond between two carbons)

The second, hexanol, has an alcohol or hidroxyl (-oh) group into the structure

The third, hexene, has an alkene group (a doble bond between two carbons)