Bromous acid
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IUPAC names
hydroxy-λ3-bromanone
hydroxidooxidobromine bromous acid |
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3D model (Jmol)
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| HBrO2 | |
| Molar mass | 112.911 g/mol |
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Other anions
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Hydrobromic acid; hypobromous acid; bromic acid; perbromic acid |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Bromous acid has the chemical formula of HBrO2. It is an unstable compounds, although salts of its conjugate base - bromites - have been isolated. In acidic solution, bromites decompose to bromine.
In 1905, Richards A. H. proved the existence of bromous acid through a series of experiments, which was conducted in the laboratory of Telluride Mill, at Colorado Spring, Co.
Using the reaction of excess cold aqueous silver nitrate (AgNO3) solution and bromine water to form hypobromous acid (HBrO), silver bromide (AgBr) and nitric acid (HNO3):
However, Richards discovered that the effect of adding excess liquid bromide in a concentrated silver nitrate (AgNO3) resulted in a different reaction mechanism. From numbers of equivalent portions of acid-bromine formed from the previous reaction, the ratio between oxygen and bromine was calculated, with the exact value of O: Br (0.149975: 0.3745), suggesting the acid compound contains two oxygen atom to one bromine atom. Thus, the chemical structure of the acid compound was deducted as HBrO2.
Richards concluded his discovery by explaining the mechanism of the overall reaction:
The formation of hypobromous acid (HBrO) first occurred when excess liquid bromide was added to concentrated silver nitrate solution. Then hypobromous acid (HBrO) was oxidized by the excess liquid bromide to form bromous acid (HBrO2)
The potential energy surface of bromous acid (HBrO2) has been investigated earlier in a view of atmospheric chemistry. The isomers of bromous acid are supported by experimental data and are applicable in current context. The molecular models of each isomer are studied with much detailed. The structure of HBrO2 is bent at the HO-oxygen with ∠(H−O−Br) angles of 106.1o. HOBrO also adopts a non-planar conformation with one isomer structure (2a) adopts a with dihedral angle ∠(H−O−Br− O) of 74.2°. Moreover, the planar structures of two other isomers (2b - cis and 2c - trans) are transition state structures for fast enantiomerization of (2a).
Another study, using the computational method, determines the equilibrium geometries of bromous acid (HBrO2) isomers using the coupled-cluster with single and double excitations and [CCSD(T)] level of theory of perturbation inclusion of triples. The study computationally calculated bond lengths and bond angles of three optimized structures of (HBrO2) isomers based on the CCSD(T)/aug-cc-pVTZ-(PP) level of theory. The picture illustrates the bond angles and bond lengths of three isomers, respectively: a. HOOBr, b. HOBrO, and c. HBr(O)O.
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