Acetals hemiketals and ketals

If you look in older texts, you may still see the terms hemiketal and ketal. At one time, four terms were used for the products of alcohols with carbonyl groups hemiacetal, acetal, hemiketal, and ketal. A hemiketal is now a type of hemiacetal and a ketal is now a type of acetal. Originally, acetals and hemiacetals came from aldehydes and ketals and hemiketals came from ketones. The structures of hemiacetals and acetals contained a C-H bond, but ketals and hemiketals did not. 

For our present purposes, we are interested in the ways in which hemi-acetals, acetals, hemiketals, and ketals are formed. Hemiacetals and hemi-ketals can be regarded as products of the addition of alcohols to the carbonyl... 

---