Skeletal formula

Skeletal formula (even frame formula ) of an organic compound is a structural formula, which allows a concise representation of the molecular structure. Skeletal formulas are ubiquitous in organic chemistry, since they can show complicated structures clearly not only, but are to be drawn quickly and easily.

The carbon skeleton

The term skeleton refers to the carbon skeleton of an organic compound that forms the main chain, side chains and / or rings of the basic organic compounds. Hydrogen atoms are the most common atoms bonded to carbon atoms, and as the carbon atoms are not explicitly depicted accurately. All other atoms are referred to as heteroatoms; they form functional groups. These are also referred to as a substituent, since, in a given molecule, carbon-bonded hydrogen atom substituting (Latin: replace ).

Implicit carbon and hydrogen atoms

In Valenzstrichformeln carbon atoms represented by the chemical symbol "C", hydrogen atom by "H". Skeletal formulas the presence and the position of these atoms are not shown, but they are automatically provided, i.e., is implied. The representation of the carbon skeleton via the drawing of the bonds between the carbon atoms. For each carbon atom of a corner is drawn.

Since carbon atoms usually form four atomic bonds, the number of added hydrogen atoms is calculated by the number of bonds of the carbon atom of 4 is subtracted. For example, the skeletal formula of hexane is shown on the right. With the " C1" labeled carbon atom has only one bond, so have three hydrogen atoms may be bound to the same carbon atom. In comparison, "C3" two hydrogen atoms must have attached, for it has formed two bonds.

The hydrogen atoms of functional groups are, however, explicitly shown. An example is the hydroxyl group of the ethanol. The functional groups to be written for the sake of clarity and compactness as a whole, without bond lines. In some cases, for example, to emphasize their role in certain reaction mechanisms, however, these are located.

Furthermore, individual hydrogen atoms are also shown if their position for a stereochemical characterization is relevant, such as the nicotine.

Explicit heteroatoms

All atoms that are not carbon or hydrogen, so all heteroatoms are shown with their chemical symbol, such as " Cl " for chlorine, "O" represents oxygen or " Na " for sodium.

Pseudo-elements

Some characters look like chemical elements, but do frequently occurring functional groups or any atom from a group dar. Often, for example, " Ph " is used for the phenyl group.

There are also:

Elements

  • X represents an arbitrary halogen atom
  • M represents any metal atom

Alkyl groups

  • R is any alkyl group or any substituent at all
  • Me represents a methyl group
  • Et for ethyl
  • N- Pr for the propyl
  • I-Pr for the isopropyl group (iso -propyl )
  • Bu for the butyl group, taking mostly the n- butyl group is meant
  • I-Bu for the isobutyl group (iso -butyl )
  • S -Bu for the sec -butyl group
  • T-Bu for tert-butyl group
  • Pn for the pentyl group, taking mostly the n- pentyl group is meant
  • Hx for the hexyl group, taking mostly the n -hexyl group is meant
  • Hp for the heptyl group, which usually n- heptyl group is meant
  • Cy for the cyclohexyl

Aromatic substituents

  • Ar for any aromatic substituent - of aryl radical - (. Ar is also the symbol for the element argon As there is currently only known to an argon compounds, there is no danger of confusion here, however )
  • Bn for the benzyl
  • Bz for the benzoyl
  • Ph is phenyl
  • Tol for the tolyl group, taking mostly the p- tolyl group (4- methylphenyl ) is meant
  • Xy for the xylyl

Functional groups

  • Ac for the acetyl (Ac is also the symbol for the element actinium. Actiniumverbindungen but are so rare that this convention can not lead to confusion )

Leaving groups

See the article leaving group for more information

  • Bs for the Brosylgruppe
  • Ns for the Nosylgruppe
  • Tf for the triflyl
  • Ts for tosyl group

Multiple bonds

Two atoms may be bound by more than a pair of electrons. Because of the geometrical and physical possibilities, single, double and triple bonds provide. Are single bonds are represented by simple lines between two atoms, the double bonds by two parallel lines and triple bonds by three parallel lines.

In more complex binding theories exist non-integer bond values ​​. In this case, a combination of solid and dashed lines is drawn, which will each represent the integer and non- integer portions of the binding.

  • Hex -3-ene having an internal carbon-carbon double bond
  • Hex -1-ene has a terminal ( final ) double bond
  • Hex - 3-in has an inner carbon-carbon triple bond
  • Hex - 1-yne has a terminal ( final ) triple bond

N.B. in the upper diagram double bonds were drawn in red and triple bonds in blue. The color coding was done just for the sake of clarity. Multiple bonds are normally displayed in color.

It is in the nature of the representation that long-chain alkanes can not be drawn linearly in the skeletal formula ( The carbon atoms are indicated by the creases between the bindings ). From the angles in the carbon chain, I can the planar representation of tetrahedral angles derived. Characterized is a formula, the skeleton of cis-trans isomerism at the double bonds occurs, always correct dar.

So in the above example, the trans and (E ) are shown configurations of the double bonds. The triple bonds are not shown tetrahedrally because its attached to carbon-carbon triple bonds, no further hydrogen atom and thus there may be no cis -trans isomerism. Right are shown two cis-and (Z)- C-C double bonds in which the carboxyl group COOH was partially drawn.

Benzene rings

Benzene rings often occur in organic compounds. To represent the delocalization of the lone pairs of the six carbon atoms in the ring, a circle is drawn in a hexagon from single bonds. This style is very common especially in textbooks.

An alternative, which is used in science often is the Kekulé structure. This style is considered to be inaccurate because they assumed three single and three double bonds (benzene would therefore cyclohexa -1 ,3,5 -triene ). However, the advantages of the representation are that can be clearly shown by their reaction mechanisms. However, the use of Kekulé representation requires the knowledge of the Elektronenpaardelokalisierung.

Stereochemistry

Stereochemical properties are represented in an appropriate manner in skeletal formulas:

  • Solid lines represent atomic bonds in the plane of representation
  • Wedge-shaped lines represent bonds that are in a higher layer, ie, in a plane which is closer to the viewer
  • Dashed lines represent bonds that lie in a deeper layer, ie, in a plane that is located farther away from the viewer
  • Curved, wavy lines represent either unknown stereochemistry or a racemic mixture of the two possible enantiomers.
  • 2-chloro -2-fluoro pentane.
  • Stereochemical skeleton of formula (R )-2 -chloro -2-fluoro pentane.
  • The skeletal formula of amphetamine that will bring its racemic nature expresses.

Other Display Types of bonds

Hydrogen bonds are sometimes indicated by dotted or dashed lines. In some cases, the addressed under stereochemistry wedge- shaped lines are also used to determine the oxidation number can. In this case the wedge points to the electronegative atom of a bond. The count is then obtained relatively simple by counting at each atom - I for each wedge and I for each peak.

Lewis structure Vertex (geometry) Cyclohexane Convention (norm) Electron pair Hexene Alkene 3-Hexyne Alkyne
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