Triple bond

A triple bond, is a form of chemical bonding between "two" atoms, which is mediated by electron pairs (→ electron pair binding). Between the atoms provide three pairs of bonding electrons the cohesion of the building upon the molecule.

Reactivity of triple bonds

A triple bond has a very high electron density and should therefore take slightly electrophilic addition reactions. In the case of carbon-carbon triple bonds, this is also true. Plays an essential role here is that C- C triple bonds are higher in energy than the C- C double or single bonds ( In the formation of a triple bond are on average 811 kJ · mol -1 free for every double bond 615 kJ · mol -1 and for each single bond 345 kJ · mol -1). This will be seen that the power output in the formation of three individual bonds instead of a single triple bond is higher. The differences are easily applied in most cases by the newly formed bonds, and it usually results in a considerable gain in energy additions to C - C triple bonds.

In nitrogen, the situation is reversed. The triple bond in the nitrogen molecule N2 with a binding energy of 945 kJ · mol -1 relatively much lower in energy ( = stable ) as a NN double bond ( upon its formation 466 kJ · mol -1 ) or even a single bond ( upon its formation only 159 kJ · mol -1 is free ). This will be seen that the power output in the formation of three individual bonds is lower rather than a single triple bond. This energy difference can not usually be applied over the formation of additional bonds with the reactants, and therefore, molecular nitrogen is a well known example of the appearance of a strong triple bond with a high stability and sluggish response behavior.

The highest binding energy ( 1077 kJ · mol -1) a triple bond, the molecule carbon monoxide (carbon monoxide, CO), since in addition to the triple bond comes to a weak ionic bond.

Orbitals of the triple bond

For quantum- chemical point of view bindings come by overlap of atomic orbitals in a molecular orbital existence. The most common description of the triple bond in alkynes via a sigma bond of sp hybrid orbital, which is between the internuclear axis, and two pi - bonds which form between them an angle of 90 degrees, and both are outside the core of the connecting axis. An alternative, completely equivalent description uses three equivalent " banana bonds ", which are formed by the overlap of sp3 hybrid orbitals.

Bond length according to Pauling

Covalent bond lengths can be estimated by Pauling as a sum of two atomic radii. On the basis of experimental data and quantum chemical additive covalent radii for atoms in triple bonds for the elements beryllium to Copernicium were published. The data set used is self-consistent and contains only one radius for all oxidation states and coordination numbers of the elements taken into account. By simply adding the atomic radii of the prediction of the triple bond length can be made ​​.

Molecules with triple bonds

Alkynes

Molecules that contain carbon-carbon triple bonds, belong to the substance group of alkynes. The chemistry of alkynes is characterized by additions of electrophiles to this binding. A party to a triple bond carbon atom is sp- hybridized, so Alkinanionen are accordingly stable and can be used as nucleophiles. The bond length of a C-C triple bond in alkynes is 120 pm.

Triple bond with boron

2012 succeeded in a working group of the University of Würzburg for the first time to produce a compound containing a stable to about 200 ° C triple bond between two boron atoms.

Triple bond with sulfur

1984 succeeded in a working group at the Free University of Berlin for the first time to synthesize a carbon-sulfur triple bond in the form of Trifluorethylidinschwefeltrifluorids. It is a colorless gas, which oligomerized quickly.