Product Code Database
In molecular geometry, bond length or bond distance is defined as the average distance between Atomic nucleus of two chemical bond in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of the molecule.
Bond lengths are measured in the solid phase by means of X-ray diffraction, or approximated in the gas phase by microwave spectroscopy. A bond between a given pair of atoms may vary between different molecules. For example, the carbon to hydrogen bonds in methane are different from those in methyl chloride. It is however possible to make generalizations when the general structure is the same.
| + Bond distance of carbon to other elements |
| group 1 |
| group 2 |
| group 2 |
| Boron group |
| group 13 |
| group 13 |
| Carbon group |
| group 14 |
| group 14 |
| group 14 |
| group 15 |
| Nitrogen group |
| group 15 |
| group 15 |
| group 15 |
| Chalcogen |
| group 16 |
| group 6 |
| group 16 |
| group 16 |
| group 6 |
| group 6 |
| Halogen |
| group 17 |
| group 17 |
| group 17 |
Unusually long bond lengths do exist. Current record holder for the longest C-C bond with a length of 180.6pm is 1,8-Bis(5-hydroxydibenzoa,dcycloheptatrien-5-yl)naphthalene, one of many molecules within a category of hexaaryl ethanes, which are derivatives based on hexaphenylethane skeleton. Bond is located between carbons C1 and C2 as depicted in a picture below.
Another notable compound with an extraordinary C-C bond length is tricyclobutabenzene, in which a bond length of 160pm is reported. Longest C-C bond within the cyclobutabenzene category is 174pm based on X-ray crystallography. In this type of compound the cyclobutane ring would force 90° angles on the carbon atoms connected to the benzene ring where they ordinarily have angles of 120°.
The existence of a very long C–C bond length of up to 290pm is claimed in a dimer of two tetracyanoethylene dianions, although this concerns a 2-electron-4-center bond. This type of bonding has also been observed in neutral phenalene dimers. The bond lengths of these so-called "pancake bonds" are up to 305pm.
Shorter than average C–C bond distances are also possible: and have bond lengths of respectively 133 and 120pm due to increased s-character of the sigma bond. In benzene all bonds have the same length: 139pm. Carbon–carbon single bonds increased s-character is also notable in the central bond of diacetylene (137pm) and that of a certain tetrahedrane (144pm).
In propionitrile the cyano group withdraws electrons, also resulting in a reduced bond length (144pm). Squeezing a C–C bond is also possible by application of steric strain. An unusual organic compound exists called In-methylcyclophane with a very short bond distance of 147pm for the methyl group being squeezed between a triptycene and a phenyl group. In an in silico experiment a bond distance of 136pm was estimated for neopentane locked up in fullerene. The smallest theoretical C–C single bond obtained in this study is 131pm for a hypothetical tetrahedrane derivative.
The same study also estimated that stretching or squeezing the C–C bond in an ethane molecule by 5pm required 2.8 or 3.5joule/mol, respectively. Stretching or squeezing the same bond by 15pm required an estimated 21.9 or 37.7kJ/mol.
| +Bond lengths in organic compounds |
| 140 |
| 134 |
| 120 |
| 130 |
|
|
