Skeletal formula 625232 226030242 2008-07-16T14:48:59Z Puppy8800 5404759 iw {{Unreferenced|chemistry related article|date=January 2007}} {{Redirect|Skeletal structure||Skeleton}} [[Image:Escitalopram-skeletal.png|thumb|right|200px|The skeletal formula of the [[antidepressant]] drug [[escitalopram]], featuring skeletal representations of [[heteroatom]]s, a [[covalent bond#Bond order|triple bond]], [[benzene|benzene rings]] and [[stereochemistry]]]] The '''skeletal formula''' of an [[organic compound]] is a shorthand representation of its [[molecular geometry|molecular structure]]. Skeletal formulae are [[wiktionary:ubiquitous|ubiquitous]] in [[organic chemistry]] because they show complicated structures clearly and they are quick and simple to draw. ==Carbon skeleton== The term skeletal refers to the ''carbon skeleton'' of an organic compound - that is, the chains, branches and/or rings of carbon atoms that form the basis of the structure of an organic molecule. The skeleton may have other atoms or groups of atoms bonded to its carbons. Hydrogen is the most common non-carbon atom bonded to carbon and is not explicitly drawn. Other atoms are known as [[heteroatom]]s and groups of atoms are called [[functional group]]s, as they give the molecule a function. Heteroatoms and functional groups are known collectively as [[substituent]]s, as they are considered to be a substitute for the hydrogen atom that would be present in the parent [[hydrocarbon]] of the organic compound in question. ==Implicit carbon and hydrogen atoms== [[Image:Skeletal-formulae-example-1-hexane.png|thumb|200px|The skeletal formula of [[hexane]]]] In standard [[chemical formula]]e, [[carbon]] [[atom]]s are represented by the symbol C and [[hydrogen]] atoms by the symbol H. In skeletal formulae, the location of carbon atoms, and hydrogen atoms bonded to carbon, are not denoted by the symbols C and H, but are [[wiktionary:implicit|implicit]]. Carbon atoms are implied to exist at each [[vertex (graph theory)|vertex]]. Carbon atoms are assumed to have four [[covalent bond]]s to them, so the number of hydrogen atoms attached to a particular carbon atom can be deduced by subtracting from four the number of bonds drawn to that carbon. For example, in the image to the right, the skeletal formula of [[hexane]] is shown. The carbon atom labelled C<sub>1</sub> has only one bond shown to it, so there must also be three hydrogens bonded to it, in order to make its total number of bonds four. The carbon atom labelled C<sub>3</sub> has two bonds to it and is therefore also bonded to two hydrogen atoms. [[Image:Ethanol-2D-skeletal.svg|thumb|200px|The skeletal formula of [[ethanol]]]] Any hydrogen atoms bonded to non-carbon atoms ''are'' drawn explicitly. In [[ethanol]], C<sub>2</sub>H<sub>5</sub>OH, for instance, the hydrogen atom bonded to oxygen is denoted by the symbol H, whereas the hydrogens bonded to carbon atoms are not shown directly. Lines representing heteroatom-hydrogen bonds are usually omitted for clarity and compactness, so a functional group like the [[hydroxyl]] group is most often written −OH instead of −O−H. These bonds are sometimes drawn out in full in order to accentuate their presence when they participate in [[reaction mechanism]]s. ==Explicit heteroatoms== All atoms that are not carbon or hydrogen are signified by their [[chemical symbol]], for instance Cl for [[chlorine]], O for [[oxygen]] and Na for [[sodium]]. These atoms are commonly known as heteroatoms in the context of organic chemistry. ==Pseudoelement symbols== There are also symbols that appear to be [[chemical symbol|chemical element symbols]], but represent certain very common substituents or indicate an unspecified member of a group of elements. These are known as pseudoelement symbols. The most widely used symbol is Ph, which represents the [[phenyl group]]. A list of pseudoelement symbols is shown below: ===Elements=== *X for any [[halogen]] atom *M for any [[metal]] atom ===Alkyl groups=== *R for any [[alkyl]] group or even any [[substituent]] at all *Me for the [[methyl group]] *Et for the [[ethyl group]] *''n''-Pr for the [[propyl]] group *''i''-Pr for the [[isopropyl]] group *Bu for the [[butyl]] group *''i''-Bu for the isobutyl group *''s''-Bu for the secondary butyl group *''t''-Bu for the tertiary butyl group *Pn for the [[pentyl]] group *Hx for the [[hexane|hexyl]] group *Hp for the [[wiktionary:heptyl|heptyl]] group *Cy for the [[cyclohexane|cyclohexyl]] group ===Aromatic substituents=== *Ar for any [[aromaticity|aromatic]] substituent *Bn for the [[benzyl]] group *Bz for the [[benzoyl]] group *Ph for the [[phenyl group]] *Tol for the [[toluene|tolyl]] group *Xy for the [[xylene|xylyl]] group ===Functional groups=== *Ac for the [[acetyl]] group ''(Ac is also the symbol for the element [[actinium]]. However, actinium is rarely encountered in organic chemistry, so the use of Ac to represent the acetyl group never causes confusion)'' ===Leaving groups=== ''See the article [[leaving group]] for further information'' *Bs for the [[tosyl|brosyl]] group *Ns for the [[tosyl|nosyl]] group *Tf for the [[triflate|trifyl]] group *Ts for [[tosyl]] group ==Multiple bonds== Two atoms can be bonded by sharing more than one pair of electrons. The common bonds to carbon are single, double and triple bonds. Single bonds are most common and are represented by a single, solid line between two atoms in a skeletal formula. Double bonds are denoted by two parallel lines, and triple bonds are shown by three parallel lines. In more advanced theories of bonding, non-[[integer]] values of [[bond order]] exist. In these cases, a combination of solid and dashed lines indicate the integer and non-integer parts of the bond order, respectively. <gallery> Image:Skeletal-formulae-internal-double-bond.png|<center>Hex-3-ene has an internal [[carbon-carbon double bond]]</center> Image:Skeletal-formulae-terminal-double-bond.png|<center>[[1-Hexene|Hex-1-ene]] has a terminal double bond</center> Image:Skeletal-formulae-internal-triple-bond.png|<center>Hex-3-yne has an internal [[alkyne|carbon-carbon triple bond]]</center> Image:Skeletal-formulae-terminal-triple-bond.png|<center>Hex-1-yne has a terminal carbon-carbon triple bond</center> </gallery> <small>''[[Nota Bene|N.B.]] in the gallery above, double bonds have been shown in red and triple bonds in blue. This was added for clarity - multiple bonds are not normally coloured in skeletal formulae.''</small> ==Benzene rings== [[Image:Benzene-circle-2D-skeletal.png|right|70px|Benzene ring with circle]] [[Benzene]] rings are very common in organic compounds. To represent the [[delocalization]] of [[electron]]s over the six carbon atoms in the ring, a circle is drawn inside the hexagon of single bonds. This style is very common in introductory organic chemistry texts used in schools. [[Image:Benzene-Kekule-2D-skeletal.png|right|70px|Kekulé structure of benzene]] An alternative style that is more common in academia is the [[Kekulé]] structure. Although it could be considered inaccurate as it implies three single bonds and three double bonds (benzene would therefore be 1,3,5-cyclohexatriene), all qualified [[chemist]]s are fully aware of the delocalization in benzene. Kekulé structures are useful for drawing [[reaction mechanism]]s clearly. ==Stereochemistry== [[Stereochemistry]] is conveniently denoted in skeletal formulae: *solid lines represent [[covalent bond|bonds]] in the plane of the paper or screen *wedges represent bonds that point out of the plane of the paper or screen, towards the observer *dashed lines represent bonds that point into the plane of the paper or screen, away from the observer *wavy lines represent either unknown stereochemistry or a [[racemic]] mixture of the two possible [[enantiomer]]s <gallery> Image:Stereochemistry-example-3D-balls.png|<center>2-chloro-2-fluoropentane</center> Image:Stereochemistry-example-2D-skeletal.png|<center>The stereochemical skeletal formula of 2-chloro-2-fluoropentane</center> Image:Stereochemistry-example-2D-skeletal-2.png|<center>The other possibility for 2-chloro-2-fluoropentane</center> Image:Amphetamine-2D-skeletal.png|<center>The skeletal formula of [[amphetamine]], showing its racemic nature</center> </gallery> ==Hydrogen bonds== [[Hydrogen bond]]s are sometimes denoted by dotted or dashed lines ==External links== * [http://www.chemguide.co.uk/basicorg/conventions/draw.html Drawing organic molecules] from ''chemguide.co.uk'' [[Category:Organic chemistry]] [[Category:Chemical formulas]] [[ar:شكل هيكلي]] [[de:Skelettformel]] [[fr:Formule topologique]] [[zh:键线式]]