Carbonyl group

A functional group consisting of a carbon atom double-bonded to an oxygen atom, written C=O. Its polarized bond gives carbonyl compounds characteristic reactivity.

Carbonyl polarity: Unequal electron distribution across a carbonyl bond, leaving its carbon partially positive and its oxygen partially negative. This charge separation makes the carbonyl carbon susceptible to nucleophilic attack.
Sigma bond: A covalent bond formed by electron density concentrated along the axis between two nuclei. The carbonyl’s carbon–oxygen double bond contains one sigma component.
Aldehyde: An organic compound containing a terminal carbonyl group bonded to hydrogen and a carbon group. Aldehydes are one major family distinguished by the carbonyl carbon’s attached hydrogen.
Imine: A functional group containing a carbon–nitrogen double bond, commonly written C=N. Replacing carbonyl oxygen with nitrogen changes bond polarity and reaction patterns.
Nucleophilic addition: A reaction in which a nucleophile bonds to an electrophilic atom, often adding across a carbon–oxygen double bond. Aldehydes and ketones commonly react by addition at the carbonyl carbon.
Pi bond: A covalent bond formed by sideways overlap of orbitals, with electron density above and below the bond axis. Its second bond component gives C=O the geometry and reactivity of a double bond.
Ketone: An organic compound whose carbonyl carbon is bonded to two carbon-containing groups. Ketones are a major carbonyl family with two carbon substituents at C=O.
Alkene: A hydrocarbon containing at least one carbon–carbon double bond. Unlike a carbonyl, an alkene double bond is usually much less polarized.
Nucleophilic acyl substitution: A reaction in which a nucleophile replaces a leaving group attached to an acyl carbon. Carboxylic acid derivatives undergo substitution because their carbonyl carbon also bears a leaving group.
Hybridization: A model that combines atomic orbitals to describe bonding orbitals and molecular geometry. The carbonyl carbon is approximately sp2-hybridized and trigonal planar.

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