Difference Between Carbonyl and Carboxyl

Carbonyl vs Carboxyl
 

Carbonyl and carboxyl are common functional groups found in organic chemistry. Both have an oxygen atom, which is double bonded to a carbon atom.

Carbonyl

Carbonyl group is a functional group with double bonded oxygen to a carbon. Aldehydes and ketones are known as organic molecules with a carbonyl group. The carbonyl group in an aldehyde always gets number one in the nomenclature as it is located at an end of the carbon chain. The carbonyl group of a ketone is always located in the middle. According to the type of the carbonyl compound, nomenclature differs. “al” is the suffix used to name aldehydes whereas “one” is the suffix used to name ketones. The carbon or carbons next to the carbonyl carbon is the α carbon/s, which have important reactivity due to the adjacent carbonyl. The carbonyl carbon atom is sp² hybridized. So aldehydes and ketones have a trigonal planar arrangement around the carbonyl carbon atom. The carbonyl group is a polar group (electronegativity of oxygen is larger than carbon, therefore, carbonyl group has a large dipole moment); thus, aldehydes and ketones have higher boiling points compared to the hydrocarbons having the same weight. Anyhow, these cannot make stronger hydrogen bonds like alcohols resulting lower boiling points than the corresponding alcohols. Because of the hydrogen bond formation ability, low molecular weight aldehydes and ketones are soluble in water. However, when the molecular weight increases, they become hydrophobic. The carbonyl carbon atom is partially positive charged, hence can act as an electrophile. Therefore, these molecules are easily subjected to nucleophilic substitution reactions. The hydrogens attached to the carbon next to the carbonyl group has acidic nature, which accounts for various reactions of aldehydes and ketones. Compounds containing carbonyl groups are widely occurring in nature. Cinnamaldehyde (in cinnamon bark), vanillin (in vanilla bean), camphor (camphor tree), and cortisone (adrenal hormone) are some of the natural compounds with a carbonyl group.

Carboxyl

Carboxyl group is a functional group in organic chemistry. This is found in carboxylic acids, hence got the name. In this, a carbon atom is double bonded to an oxygen atom and connected to a hydroxyl group with a single bond. It is shown as –COOH. The carbon atom can form another bond with an atom besides these groups. Therefore, carboxyl group can be a part of a large molecule. Carboxyl is an acidic group. It acts as a weak acid and at high pH values it dissociates. Because of the –OH group, they can form strong hydrogen bonds with each other and with water. As a result, molecules with the carboxyl group have high boiling points. When carboxyl group is in a molecule as the functional group, it is given number one in the nomenclature and name ends with “oic acid.” Carboxyl functional group is common in biological systems, as well. Amino acids have a carboxyl group or sometimes more than one carboxyl group.