Carbonyl group

Ketone-general

Aldehyd - Aldehyde

Ketone-general

Carboxylic-acid

Ester

Carbonyl group is a functional group in organic chemistry consisting of a carbon atom double-bonded to an oxygen atom (C=O). The simplest carbonyl groups are aldehydes and ketones, but they are also found in carboxylic acids, esters, amides, and other compounds. The carbonyl group is a fundamental moiety in organic synthesis and is ubiquitous in biochemistry, playing a critical role in the structure and function of many biomolecules.

Structure and Bonding

The carbonyl carbon and oxygen atoms share a double bond, which consists of one sigma (σ) bond and one pi (π) bond. The π bond is formed by the sideways overlap of p orbitals, allowing for the delocalization of electrons, which contributes to the reactivity of the carbonyl group. The carbon and oxygen in the carbonyl group have a significant difference in electronegativity, leading to a polar bond. This polarity makes the carbonyl carbon an electrophilic site and the oxygen a nucleophilic site, influencing the group's chemical reactivity.

Reactivity

The reactivity of the carbonyl group is largely due to its polar nature and the presence of the π bond. Nucleophiles can attack the electrophilic carbon, leading to the addition or substitution reactions that are central to carbonyl chemistry. The outcome of such reactions depends on the nature of the carbonyl compound and the conditions of the reaction. For example, aldehydes and ketones undergo nucleophilic addition reactions, while carboxylic acid derivatives typically undergo nucleophilic acyl substitution.

Types of Carbonyl Compounds

• Aldehydes: Compounds with a carbonyl group bonded to at least one hydrogen atom. Aldehydes are typically more reactive than ketones due to the presence of the hydrogen atom, which makes the carbonyl carbon more electrophilic.
• Ketones: Carbonyl compounds where the carbonyl group is bonded to two carbon atoms. Ketones are less reactive than aldehydes due to steric hindrance and the electron-donating effects of the alkyl groups.
• Carboxylic Acids: Organic acids containing a carbonyl group bonded to a hydroxyl group. They are known for their acidity, which is due to the ability of the hydroxyl hydrogen to dissociate, leaving a resonance-stabilized carboxylate anion.
• Esters: Derived from carboxylic acids and alcohols, esters contain a carbonyl group bonded to an oxygen atom that is, in turn, bonded to another carbon atom. Esters are known for their distinctive fragrances and flavors.
• Amides: Result from the condensation of a carboxylic acid and an amine. Amides contain a carbonyl group bonded to a nitrogen atom and are key components of proteins.

Applications

Carbonyl compounds are ubiquitous in organic synthesis, serving as key intermediates in the synthesis of alcohols, acids, esters, and many other functional groups. In biochemistry, many biomolecules, such as sugars and amino acids, contain carbonyl groups, which are critical for the structure and function of proteins and nucleic acids. The carbonyl group is also instrumental in the pharmaceutical industry, where many drugs contain carbonyl moieties due to their reactivity and ability to form stable compounds.

See Also

• Organic synthesis
• Nucleophilic addition
• Nucleophilic acyl substitution
• Electrophilicity
• Polarity (chemistry)

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