The "hemi" structure is not found exclusively in carbohydrates but in other organic molecules as well. The most general representation of the structure is:
If R' is a hydrogen atom, the structure is called a hemiacetal:
If R' is a carbon containing group, it is a hemiketal. In cyclized ketoses the R' group is always CH2OH:
Now compare these general structures to the cyclized carbohydrate molecules as we saw them on the previous page. Some of the atoms are colored to make it easier.
