Symmetric hydrogen bond

A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a 3-center 4-electron bond. This type of bond is much stronger than "normal" hydrogen bonds, in fact, its strength is comparable to a covalent bond. It is seen in ice at high pressure (Ice X), and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the bifluoride ion [F−H−F]⁻. Much has been done to explain the symmetric hydrogen bond quantum-mechanically, as it seems to violate the duet rule for the first shell: The proton is effectively surrounded by four electrons. Because of this problem, some consider it to be an ionic bond.

References

Steiner, Thomas (2002). "The Hydrogen Bond in the Solid State". Angewandte Chemie International Edition. 41: 48. doi:10.1002/1521-3773(20020104)41:1<48::AID-ANIE48>3.0.CO;2-U.

Chemical bonds

Intramolecular
("strong")

Covalent bond

By symmetry	Sigma (σ) Pi (π) Delta (δ) Phi (φ)

By multiplicity	1 (single) 2 (double) 3 (triple) 4 (quadruple) 5 (quintuple) 6 (sextuple)

Miscellaneous	Agostic bond Bent bond Dipolar bond Pi backbond Charge-shift bond Hapticity Conjugation Hyperconjugation Antibonding

Resonant bonding	Electron deficiency 3c–2e 4c–2e Hypercoordination 3c–4e Aromaticity möbius super sigma homo spiro σ-bishomo spherical Y-

Metallic bonding

Metal aromaticity

Ionic bonding

Intermolecular
("weak")

van der Waals forces	London dispersion force

Hydrogen bond	Low-barrier Resonance-assisted Symmetric Dihydrogen bonds C–H···O interaction

Other noncovalent	Mechanical bond Halogen bond Aurophilicity Intercalation Stacking Cation–pi bond Anion–pi bond Salt bridge

This article is issued from Wikipedia - version of the 3/14/2013. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.