The carbon atom is attached to a hydrogen atom on one side and an R group (which may be another
H atom in the case of formaldehyde) on the other.
Ketones
The carbon atom is attached to two R groups that are not hydrogen atoms.
Esters
The carbonyl carbon atom in an ester is bonded to an R group on one side and an OR’ group (that is
not OH) on the other.
Carboxylic acids
The carbon atom is attached to an R group and a hydroxyl (–OH) group. Like alcohols that also
contain the hydroxyl group, carboxylic acids can participate in hydrogen bonding. These
compounds are weak acids (weak compared with inorganic acids like HCl) because the hydroxyl
hydrogen can be donated as a proton. Fatty acids, for example, are carboxylic acids with a long
hydrocarbon chain (the R group attached to the carbonyl carbon is a long hydrocarbon). After the
donation of a proton, the carboxylic group left behind has a negative charge and is thus attracted to
a polar medium. The hydrocarbon chain, on the other hand, is nonpolar. In aqueous solution,