Banana bonds or bent bonds ^{[1] [2] [3]} 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. A chemical bond is the physical phenomenon (or phenomena) responsible for the attractive interactions betwen atoms that confers stability to di- and polyatomic chemical compounds. ... In chemistry, hybridisation is the mixing of atomic orbitals to form new orbitals suitable for bonding. ... Electron configuration is the arrangement of electrons in an atom, molecule or other body. ... Geometry of the water molecule Molecular geometry or molecular structure is the three dimensional arrangement of the atoms that constitute a molecule, inferred from the spectroscopic studies of the compound. ... Benzene An organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with the exception of carbides, carbonates, carbon oxides and elementary carbon. ... Molecule structure formula of cyclopropane Cyclopropane is a cycloalkane molecule with the molecular formula C3H6 consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms. ... The chemical compound ethylene oxide is an important industrial chemical used as an intermediate in the production of ethylene glycol and other chemicals, and as a sterilant for foodstuffs and medical supplies. ... Aziridine parent compound Aziridines are a group of organic compounds sharing the aziridine functional group which is a three membered heterocycle with one amine group and two methylene groups 1,2. ...

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°. This bending can be observed experimentally by X-ray diffraction of certain cyclopropane derviatives: the deformation density is outside the line of centers between carbons. The carbon carbon bond lengths are unusually short: 151 pm versus 154 pm for a regular bond. Geometry of the water molecule Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... In molecular geometry, bond length or bond distance is the distance between two bonded atoms in a molecule. ... Picometre (American spelling: picometer) is an SI measure of length that is equal to 10−12 of a metre. ...

One of the first bent bond theories for cyclopropane was the so-called Coulson-Moffitt model (1947).

Cyclobutane is a larger ring but still has bent bonds. In this molecule the carbon bond angles are 96° for the planar conformation and 88° for the puckered one. Contrary to cyclopropane the CC bond lengths actually increase and not decrease and this is mainly due to 1,3-nonbonded steric repulsions. In terms of reactivity cyclobutane is relatively inert and behaves like ordinary alkanes. Image File history File links Coulson_Moffit_Model. ... Cyclobutane, C4H8, with a molecular mass of 56. ... An alkane is an acyclic saturated hydrocarbon. ...

The bent bond theory can also explain other phenomena in organic molecules. In fluoromethane (CH₃F) for instance the experimental F-C-H bond angle is 109° but should be less. This is due to the fact that according to Bent's rule, the C-F bond gains p-orbital character leading to high s-character in the C-H bonds and H-C-H bond angles approaching that of sp₂ orbitals e.g. 120° leaving less for the F-C-H bond angle. The difference is again explained in terms of bent bonds. Fluoromethane, also known as methyl fluoride, Freon 41 and HFC-41, is a toxic, liquefiable, and flammable gas at standard temperature and pressure. ... Bents rule, which concerns orbital hybridisation of chemical bonds, was stated in 1961 by the American chemist Henry Bent [1]. Originally, it was expressed as follows: Atomic s character concentrates in orbitals directed toward electropositive subsituents In other words, more understandable in terms of p-character of hybridized bonds...

Bent bonds also come into play in the gauche effect explaining the preference for gauche conformations in certain substitutend alkanes and the cis effect associated with some unusually stable alkene cis isomers. In stereochemistry, gauche interactions hinder bond rotation. ... Cis-2-butene Trans-2-butene In chemistry, geometric isomerism or cis-trans isomerism is a form of stereoisomerism and describes the orientation of functional groups within the molecule. ... In chemistry, geometric isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. ...

Other models

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For cyclopropane, the banana bond model continues to have support despite the emergence of other theories such as Walsh orbitals, which aimed to do a better job fitting molecular orbital theory in light of spectroscopic evidence and group symmetry arguments. Critics of the Walsh orbital theory argue that this model does not represent the ground state of cyclopropane^{[verification needed]}. There have been attempts to "repair" the walsh orbital theory but this has largely met with resistance; Walsh orbitals may still explain bonding in other molecules of interest. Image File history File links Unbalanced_scales. ... Image File history File links Circle-question. ... In quantum chemistry, molecular orbitals are the statistical states electrons can have within molecules. ...

External links

• NMR experiment

References

1. ^ Burnelle, L.; Kaufmann, J.J. J.Chem. Phys. 1965, 43 , 3540;Klessinger, M. J. Chem. Phys.1967, 46 , 3261
2. ^ Bent Bonds in Organic Compounds Kenneth B. Wiberg Acc. Chem. Res.; 1996; 29(5) pp 229 - 234; (Article) DOI:10.1021/ar950207a
3. ^ Advanced Organic Chemistry F.A. Carey R.J. Sundberg ISBN 0-306-41198-9