Bond length
You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.
In molecular geometry, bond length or bond distance is the average distance between nuclei of two bonded atoms in a molecule.
Contents |
Explanation
Bond length is inversely related to bond order, when more electrons participate in bond formation the bond will get shorter. Bond length is also inversely related to bond strength and the bond dissociation energy, as a stronger bond is also a shorter bond. In a bond between two identical atoms half the bond distance is equal to the 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 single bonds for carbon to other elements is given below. Bond lengths are given in picometers. By approximation the bond distance between two different atoms is the sum of the individuales covalent radii (these are given in the chemical element articles for each element). As a general trend, bond distances decrease across the row in the periodic table and increase down a group. This trend is identical to that of the atomic radius.
| H | 106 - 112 | group 1 |
| Be | 193 | group 2 |
| Mg | 207 | group 2 |
| B | 156 | group 13 |
| Al | 224 | group 13 |
| In | 216 | group 13 |
| C | 154 - 120 | group 14 |
| Si | 186 | group 14 |
| Sn | 214 | group 14 |
| Pb | 229 | group 14 |
| N | 147 - 210 | group 15 |
| P | 187 | group 15 |
| As | 198 | group 15 |
| Sb | 220 | group 15 |
| Bi | 230 | group 15 |
| O | 143 - 215 | group 16 |
| S | 181 - 255 | group 16 |
| Cr | 192 | group 6 |
| Se | 198 - 271 | group 16 |
| Te | 205 | group 16 |
| Mo | 208 | group 6 |
| W | 206 | group 6 |
| F | 134 | group 17 |
| Cl | 176 | group 17 |
| Br | 193 | group 17 |
| I | 213 | 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 orbital hybridisation and the electronic and steric nature of 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, tricyclobutabenzene, a bond length of 160 pm is reported. The current record holder is another cyclobutabenzene with length 174 pm based on X-ray crystallography [1]. 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 [1] [1]. This type of bonding has also been observed in dimers of neutral phenalene dimers. The bond lengths of these so-called pancake bonds [1] are up to 305 pm.
Shorter than average carbon carbon bonds distances are also possible, alkenes and alkynes have bond lengths of respectively 133 and 120 pm due to increased s-character of the sigma bond.In benzene all bonds have the same length: 139 pm. In carbon carbon single bonds increased s-character is also notable in the central bond of diacetylene (137 pm) and that of a certain tetrahedrane dimer (144 pm).
In propionitrile the cyano group withdraws electrons also resulting in a reduced bond length (144 pm). Squeezing a CC bond is also possible by application of strain. An unusual organic compound exists called In-Methylcyclophane with a very short bond distance of 147 pm for the methyl group being squeezed between a trypticene and a phenyl group. In an in silico experiment a bond distance of 136 pm is estimated for neopentane locked up in fullerene [1]. The smallest theoretical CC single bond obtained in this study is 132 pm for a hypothetical adamantane like molecule.
In the same study it is estimated that for ethane it takes 2.8 kJ/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 [1] | |||||
|---|---|---|---|---|---|
| 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 | ||||
External links
- Utah Chemists Find Longest Carbon-Carbon Bond Press release
References
External links
de:Bindungslänge nl:Bindingslengte
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
