Nature of Carbonyl Group

The carbonyl group is chemically the organic functional group that consists of the carbon atom which has a double bond with the oxygen atom. The simplest carbonyl groups are the ketones and aldehydes. They are usually joined with other carbon compounds. In any aromatic compound, their structure can be found and they have major participation in the taste and the scent of the aromatic compounds. The state where carbon along with oxygen makes a double bond is termed as the carbonyl group entity and the carbonyl compounds are the members of the carbonyl group. 

CARBONYL GROUP

As per organic chemistry, a divalent chemical unit consisting of one carbon (C) and one oxygen (O) atom which is connected by a double bond is a carbonyl group. A carbonyl group is an essential group of carboxylic acids, esters, anhydrides, acyl halides, amides, and quinones, and it is the characteristic reactive group of aldehydes and ketones. Carboxylic acids along with their derivatives, aldehydes, ketones, and quinones are jointly known as carbonyl compounds.

The oxygen atom in the carbonyl group shares two out of its six valence electrons with the carbon atom in the carbonyl group. The balance of four valence electrons remains as two sets of lone pairs of electrons. The carbon atom in the carbonyl group shares two out of its four valence electrons with the oxygen atom of the carbonyl group, and the remaining two electrons create two single bonds with other atoms. The simplest compound with a carbonyl group is formaldehyde (CH2O).

STRUCTURE OF CARBONYL GROUP

The carbonyl carbon atom which is sp2-hybridized participates in contributing one electron to the three hybrid orbitals, forming three sigma bonds. Formaldehyde has two sigma bonds with hydrogen bonds and one sigma bond with the oxygen atom in the carbonyl group. These coplanar bonds stand at nearly 120° to each other. The fourth electron of the carbonyl carbon atom resides in a 2p orbit which is perpendicular to the plane of the orbitals of three sp2-hybrid. 

The carbonyl oxygen atom or sp2-hybridized participates in contributing one of its six valence electrons to the sp2-hybrid orbital that creates a sigma bond with the carbon atom of the carbonyl group. Four valence electrons remain as two sets of unbonded pairs of electrons in the other two sp2-hybrid orbitals. They stand in the same plane nearly 120° to each other and the carbon-oxygen bond. The last valence electron resides in a 2p orbital which is perpendicular to the plane of the sp2-hybrid orbitals. The 2p orbitals of the carbon and oxygen atoms intersect each other to form a pi bond.

CARBONYL COMPOUNDS

Carbonyl compounds are molecules that consist of the carbonyl group, where carbon and oxygen atoms are joined in with a double covalent bond, C=O. Acetaldehyde (CH3CHO), which belongs to the carbonyl group is found to be abundant in the atmosphere and also expelled out during the combustion and photooxidation of hydrocarbons. Simply stated, the compounds contained in the carbonyl group are commonly referred to as carbonyl compounds. 

The carbonyl group has a structure characteristic of many various types of compounds. The carbonyl compound is among one of the many classes of organic compounds that contribute to many larger functional groups. The carbonyl compound is found present in carbon dioxide and methanol, which represents the extreme upper and lower levels of carbonyl carbon oxidation, respectively. In interference to this, many carbonyl compounds including aldehydes and ketones, and their derivatives like esters, amides, anhydrides, acid halides are formed.

EXAMPLES OF CARBONYL COMPOUNDS

The various examples of carbonyl compounds are as follows:

Aldehydes

Aldehyde is among the class of organic compounds in which a carbon atom shares a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms. The double bond between carbon and oxygen is a feature of all aldehydes and thus it is known to be a member of the carbonyl group. Many aldehydes have pleasing odors, and they are prepared from alcohols by removal of hydrogen or simply known as the process of dehydrogenation. The aldehydes get their name from this process.

Ketones

Ketone is the class of organic compounds that are considered by the existence of a carbonyl group in which the carbon atom is joined with the oxygen atom through covalent bonds. Ketone compounds have significant functional properties. They occur in several sugars and compounds used for the preparation of medicines, including natural and synthetic steroid hormones. Many complex organic compounds are formed chemically using ketones as blocks for formation. They are most commonly used as solvents, generally in industries manufacturing explosives, lacquers, paints, and textiles. Ketones are also used in tanning, as preservatives, and in hydraulic fluids.

Carboxylic Acid

Carboxylic acid is the class of compounds found organically in which a carbon atom is bonded to an oxygen atom by a double covalent bond and a hydroxyl group by a single covalent bond. A fourth bond joins the carbon atom to a hydrogen atom or some other combining group of single valency. The carboxyl (COOH) group is named because of the carbonyl group (C=O) and a hydroxyl group. Carboxylic acids are abundantly found in nature. The fatty acids consist of glycerides, which are ultimately the components of fat. Hydroxyl acids, for example, lactic acid which is found in sour-milk products like yogurt, and citric acid that is found in citrus fruits like orange, and many keto acids are significant metabolic products that are found in most living cells. Proteins are made up of amino acids, which also contain carboxyl groups.

Carbonate Ester

Carbonate ester or organic carbonate is a chemical compound derived from carbonic acid. This functional group consists of a carbonyl group edged by two alkoxy groups. Monomers of polycarbonates are linked by carbonate groups. These polycarbonates are used in lenses of eyeglass, compact discs, and bulletproof glass. Carbonate esters like dimethyl carbonate, ethylene carbonate, propylene carbonate which are small are used as solvents. Dimethyl carbonate is also a mild methylation agent.

CONCLUSION

In this article, we have discussed the carbonyl group as the organic functional group that consists of the carbon atom which has a double bond with the oxygen atom. The state where carbon along with oxygen makes a double bond is termed as the carbonyl group entity and the carbonyl compounds are the members of the carbonyl group. 

We have also learned about the structure of the carbonyl group as formaldehyde has two sigma bonds with hydrogen bonds and one sigma bond with the oxygen atom in the carbonyl group. Also, the various examples of carbonyl compounds like aldehydes, ketones, carboxylic acid, etc.