Editing Ketone (section)

==Structure and bonding==
[[File:KetoneVarietyPack.png|thumb|600px|center|Representative ketones, from the left: [[acetone]], a common solvent; [[Oxaloacetic acid|oxaloacetate]], an intermediate in the [[Krebs Cycle|metabolism of sugars]]; [[acetylacetone]] in its (mono) enol form (the enol highlighted in blue); [[cyclohexanone]], precursor to [[nylon]]; [[muscone]], an animal scent; and [[tetracycline]], an antibiotic]]

The ketone carbon is often described as [[Orbital hybridisation#sp2|sp<sup>2</sup> hybridized]], a description that includes both their electronic and molecular structure. Ketones are [[trigonal planar]] around the ketonic carbon, with C–C–O and C–C–C bond angles of approximately 120°. Ketones differ from [[aldehyde]]s in that the carbonyl group (C=O) is bonded to two carbons within a [[carbon skeleton]]. In aldehydes, the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains. Ketones are also distinct from other carbonyl-containing [[functional group]]s, such as [[carboxylic acid]]s, [[ester]]s and [[amide]]s.<ref>{{McMurry3rd}}</ref>

The carbonyl group is [[polar molecule|polar]] because the electronegativity of the oxygen is greater than that for carbon. Thus, ketones are [[nucleophilic]] at oxygen and [[electrophilic]] at carbon. Because the carbonyl group interacts with water by [[hydrogen bond]]ing, ketones are typically more soluble in water than the related methylene compounds. Ketones are hydrogen-bond acceptors. Ketones are not usually hydrogen-bond donors and cannot hydrogen-bond to themselves. Because of their inability to serve both as hydrogen-bond donors and acceptors, ketones tend not to "self-associate" and are more volatile than alcohols and [[carboxylic acid]]s of comparable [[molecular weight]]s. These factors relate to the pervasiveness of ketones in perfumery and as solvents.

===Classes of ketones===
Ketones are classified on the basis of their substituents. One broad classification subdivides ketones into symmetrical and unsymmetrical derivatives, depending on the equivalency of the two organic substituents attached to the carbonyl center. Acetone and [[benzophenone]] ({{chem2|(C6H5)2CO}}) are symmetrical ketones. [[Acetophenone]] {{chem2|(C6H5C(O)CH3)}} is an unsymmetrical ketone.

====Diketones====
{{main|dicarbonyl}}
Many kinds of diketones are known, some with unusual properties. The simplest is [[diacetyl]] {{chem2|(CH3C(O)C(O)CH3)}}, once used as butter-flavoring in [[popcorn]]. [[Acetylacetone]] (pentane-2,4-dione) is virtually a misnomer (inappropriate name) because this species exists mainly as the monoenol {{chem2|CH3C(O)CH\dC(OH)CH3}}. Its enolate is a common ligand in [[coordination chemistry]].

====Unsaturated ketones====
Ketones containing [[alkene]] and [[alkyne]] units are often called unsaturated ketones. A widely used member of this class of compounds is [[methyl vinyl ketone]], {{chem2|CH3C(O)CH\dCH2}}, a  [[α,β-Unsaturated carbonyl compound|α,β-unsaturated carbonyl compound]].

====Cyclic ketones====
Many ketones are cyclic. The simplest class have the formula {{chem2|(CH2)_{''n''}CO}}, where ''n'' varies from 2 for [[cyclopropanone]] ({{chem2|(CH2)2CO}}) to the tens. Larger derivatives exist. [[Cyclohexanone]] ({{chem2|(CH2)5CO}}), a symmetrical cyclic ketone, is an important intermediate in the production of [[nylon]]. [[Isophorone]], derived from acetone, is an unsaturated, asymmetrical ketone that is the precursor to other [[polymer]]s. [[Muscone]], 3-methylpentadecanone, is an animal [[pheromone]]. Another cyclic ketone is [[cyclobutanone]], having the formula {{chem2|(CH2)3CO}}.