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.
Energy profiles for different hydrogen bond types between oxygen heteroatoms. Standard hydrogen bonds are asymmetrical, with the hydrogen being associated with one heteroatom. When the pKa between the heteroatoms is equal, a symmetrical hydrogen bond forms with the hydrogen properly between two locations. At shorter distances, the barrier between the two energy minima is low enough that the hydrogen is equally bound as a low-barrier, or single-well hydrogen bond.
Referencesedit
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.
January 01, 1970
symmetric, hydrogen, bond, symmetric, hydrogen, bond, special, type, hydrogen, bond, which, proton, spaced, exactly, halfway, between, identical, atoms, strength, bond, each, those, atoms, equal, example, center, electron, bond, this, type, bond, much, stronge. 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 Energy profiles for different hydrogen bond types between oxygen heteroatoms Standard hydrogen bonds are asymmetrical with the hydrogen being associated with one heteroatom When the pKa between the heteroatoms is equal a symmetrical hydrogen bond forms with the hydrogen properly between two locations At shorter distances the barrier between the two energy minima is low enough that the hydrogen is equally bound as a low barrier or single well hydrogen bond References editSteiner Thomas 2002 The Hydrogen Bond in the Solid State Angewandte Chemie International Edition 41 48 doi 10 1002 1521 3773 20020104 41 1 lt 48 AID ANIE48 gt 3 0 CO 2 U Retrieved from https en wikipedia org w index php title Symmetric hydrogen bond amp oldid 944794335, wikipedia, wiki, book, books, library,
