Hemiacetal, Hemiketal, and Acetal Functional Groups:
In the simplest form, the hemiacetal is really the
combination of two functional groups. A hemiacetal is an alcohol
and ether ATTACHED TO THE SAME CARBON. The fourth bonding position
is occupied by a hydrogen. A hemiacetal is derived from an aldehyde.
A hemiketal is an alcohol and ether attached to the
same carbon, along with two other carbons. A hemiketal is derived
from a ketone.
An acetal is two ether groups ATTACHED TO THE SAME
CARBON. The acetal is derived from a hemiacetal and an alcohol
making the second ether group.
A hemiacetal plus an alcohol yields an acetal. At the simplest
level this is really the reaction of an alcohol plus alcohol
reaction to form an ether.
General Equation for Acetal Formation:
Hemiacetal + Alcohol <===> Acetal + HOH
The acetal group can be recognized by finding a carbon with
TWO ether functional group attached to it.