Bond length



In molecule.

Explanation

Bond length is inversely related to covalent radius. Bond lengths are measured in molecules by means of x-ray diffraction. A set of two atoms sharing a bond is unique going from one molecule to the next. For example the carbon to hydrogen bond in methane is different from that in methyl chloride. It is however possible to make generalizations when the general structure is the same.

Bond lengths of carbon with other elements

A table with experimental atomic radius.

H106 - 112group 1
group 2
group 2
B156group 13
Al224group 13
In216group 13
group 14
group 14
group 14
group 14
group 15
group 15
group 15
group 15
group 15
group 16
group 16
Cr192group 6
group 16
group 16
Mo208group 6
W206group 6
group 17
group 17
group 17
group 17
Table 1. Bond distance of carbon to other elements in picometers [1]

Bond lengths in organic compounds

The actual bond length between two atoms in a molecule depends on such factors as the substituents. The carbon carbon bond length in diamond is 154 pm which is also the largest bond length that exists for ordinary carbon covalent bonds.

Unusually long bond lengths do exist. In one, X-ray crystallography [2]. In this type of compounds 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 290 pm is claimed in a dimer of two tetracyanoethylenedianions although this concerns a 2-electron-4-center bond [3] [4]. This type of bonding has also been observed in dimers of neutral phenalene dimers. The bond lengths of these so-called pancake bonds [5] are up to 305 pm.

Shorter than average carbon carbon bonds distances are also possible, tetrahedrane dimer (144 pm).

In propionitrile the adamantane like molecule.

In the same study it is estimated that for mol to stretch the CC bond by 5 pm from its equilibrium value and only 3.5 kJ/mol to squeeze it by the same amount. on the other hand, stretching and squeezing by 15 pm requires 21.9 and 37.7 kJ/mol.

Bond lengths in organic compounds [7]
C-H length (pm) C-C length (pm) Multiple bonds length (pm)
sp3-H 110 sp3-sp3 154 Benzene 140
sp2-H 109 sp3-sp2 150 Alkene 134
sp-H 108 sp2-sp2 135 Alkyne 120
sp3-sp 146 Allene 130
sp2-sp 143
sp-sp 120

References

  1. ^ Handbook of Chemistry & Physics 65th Edition CRC Press ISBN 0-8493-0465-2
  2. ^ Naphthocyclobutenes and Benzodicyclobutadienes: Synthesis in the Solid State and Anomalies in the Bond Lengths Fumio Toda European Journal of Organic Chemistry Volume 2000, Issue 8, Date: April 2000, Pages: 1377-1386 Abstract
  3. ^ Exceptionally Long (2.9 Å) C-C Bonds between [TCNE]- Ions: Two-Electron, Four-Center *-* C-C Bonding in -[TCNE]22- Angewandte Chemie International Edition Volume 40, Issue 13, Date: July 2, 2001, Pages: 2540-2545 Juan J. Novoa, Pilar Lafuente, Rico E. Del Sesto, Joel S. Miller Abstract
  4. ^ Stable (Long-Bonded) Dimers via the Quantitative Self-Association of Different Cationic, Anionic, and Uncharged -Radicals: Structures, Energetics, and Optical Transitions Jian-Ming Lü, Sergiy V. Rosokha, and Jay K. Kochi J. Am. Chem. Soc.; 2003; 125(40) pp 12161 Abstract
  5. ^ Aromaticity on the Pancake-Bonded Dimer of Neutral Phenalenyl Radical as Studied by MS and NMR Spectroscopies and NICS Analysis Shuichi Suzuki, Yasushi Morita, Kozo Fukui, Kazunobu Sato, Daisuke Shiomi, Takeji Takui, and Kazuhiro Nakasuji J. Am. Chem. Soc.; 2006; 128(8) pp 2530 Abstract
  6. ^ Squeezing CC Bonds Deborah R. Huntley, Georgios Markopoulos, Patrick M. Donovan, Lawrence T. Scott, Roald Hoffmann Angewandte Chemie International Edition Volume 44, Issue 46 , Pages 7549 - 7553 2005
  7. ^ Fox, MA and JK Whitesell. Organische Chemie. 1994. Spektrum
 
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