Banana bond
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Banana bonds or bent bonds [1] [2] are a special type of chemical bonding in which the ordinary hybridization state of two atoms making up a chemical bond are modified with increased or decreased s-orbital character in order to accommodate a particular molecular geometry. Bent bonds are found in strained organic compounds such as cyclopropane, oxirane and aziridine. In these compounds it is not possible for the carbon atoms to assume the 109.5° bond angles with standard sp3 hybridization. Increasing the p character makes it possible to reduce the bond angles to 60°. At the same time the carbon to hydrogen bonds gain more s-character and shorten. In cyclopropane the maximum electron density between two carbon atoms does not correspond to the internuclear axis hence the name bent bond. In cyclopropane the interorbital angle is 104°.
For cyclopropane, the banana bond model has largely been thrown out in favor of walsh orbitals, which better fits molecular orbital theory in light of spectroscopic evidence and group symmetry arguments. There have been attempts to "repair" the banana bond theory but this has largely met with resistance; banana bonds may still explain bonding in other molecules of interest.
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References
- ↑ Burnelle, L.; Kaufmann, J.J. J.Chem. Phys. 1965, 43 , 3540;Klessinger, M. J. Chem. Phys.1967, 46 , 3261
- ↑ Advanced Organic Chemistry F.A. Carey R.J. Sundberg ISBN 0306411989
