H is a functional group
present in amino acids
and carboxylic acids
. Its structure is composed of one carbon atom attached to an oxygen atom by a double bond
and to a hydroxyl group
by a single bond
. It is often mentioned that a carboxyl group is a carbonyl group
bonded to a hydroxyl
group. The carboxyl group has one valence electron
in its carbon atom, making it possible to be a part in a larger molecule
by bonding through it. Carboxyl groups can only occur at the end of a carbon chain, because the carbon must make 3 bonds (O double bond and single bond to hydroxyl group) in addition to its connection to the R group.
Carboxyl groups will often lend their OH H+ into solution and therefore will act as acids. This is the case with carboxylic acids, such as is the case when acetic acid lends its H+ into solution to become acetate.