In chemistry, the oxocarbon anion is a negative ion composed of only carbon and oxygen atoms, and therefore has the general formula C
n -
y for some integers x , y , and n .
The most common oxocarbon anions are carbonates, CO 2 -
3 , and oxalate, C sub style = "font size: inherit; line-height: inherit; vertical-align: baseline"> 2 2 -
4 > . There are however a large number of stable anions in this class, including some that have research or industrial use. There are also many unstable anions, such as CO -
2 and CO -
4 , which has a fleeting existence during several chemical reactions; and many hypothetical species, such as CO 4 - 4 , which has been the subject of theoretical studies but not yet observed.
A stable oxicarbon anion forms salt with various cations. Unstable anions can survive in very clear gas conditions, such as in interstellar clouds. Most oxycarbon anions have the corresponding groups in organic chemistry, which are usually ester compounds. Thus, for example, the oxalate group [-O- (C = O) 2 -O-] occurs in the dimethyl oxalate ester H 3 CO- (C = O) 2 -O-CH 3 .
Video Oxocarbon anion
Distributed cost and resonance
In many oxocarbon anions any extra electrons responsible for negative electrical charges behave as if distributed to multiple atoms. Some pairs of electrons responsible for covalent bonds also behave as if they are delocalized. This phenomenon is often described as resonance between two or more different conventional molecular structures at the location of the charge and the bond. Carbon ions, for example, are considered to have "average" of three different structures:
so each oxygen has the same negative charge equivalent to 2 / 3 of an electron, and each CO bond has the same average valence 4 / 3 . This model contributes to three symmetries of the observed anions.
Similarly, in the carboxyl group deprotonation - CO - 2 , each oxygen is often assumed to have a charge - 1 / 2 and each CO bond has a valency of 3 / 2 , so the two oxygen equivalent. Anion croconate C
5 O 2 -
5 also has five times symmetry, which can be described as a superposition of five statuses that lead to payload - 2 / 5 on each oxygen. This resonance is believed to contribute to anion stability.
Maps Oxocarbon anion
Related compound
Oxocarbonic acid
Anion oksokarbon C
x O n - y can be seen as a result of removing all protons from an appropriate acid C x y . Carbonate CO 2 - 3 , for example, can be seen as carbonic acid anion H 2 CO 3 . Sometimes "acid" is actually an alcohol or other species; this is the case, for example, from acetylenediolate C
2 O 2 -
2 which will generate acetylenediol C 2 H 2 O 2 . However, anions are often more stable than acids (as is the case for carbonates); and sometimes the acid is unknown or thought to be very unstable (as does methanetetracarboxylate C (COO - ) 4 ).
Neutralized Species
Each an oxocarbon anion C
x O n - y can be matched principally to neutral (or oxidized) electricity ) variant C x , oxygen (carbon oxide) with the same composition and structure except for the negative charge. As a rule, however, these neutral oxocarbons are less stable than the corresponding anions. Thus, for example, a stable carbonate anion corresponds to a highly unstable carbon neutral CO trioxide 3 ; oxalate C
2 O 2 -
4 according to 1,2-dioxetanedione C less stable 2 O 4 ; and the croconate anion is stable C
5 O 2 -
5 corresponds to the cyclopentanepentone neutral C 5 O 5 , which has been detected in only a small amount.
Reduce variant
In contrast, some oxocarbon anions can be reduced to produce another anion with the same structural formula but larger negative charges. So rhodizonate C
6 O 2 -
6 can be reduced to anion tetrahydroxybenzoquinone (THBQ) C
6 O 4 -
6 and then to benzenehexolate C
6 O 6 -
6 .
Acid anhydride
Anion oksokarbon C
x O n - y may also be associated with anhydride of the corresponding acid. The latter will be another oxocarbon with the formula C x O y - n / 2 ; that is, the minus acid n / 2 water molecule H 2 O. The standard example is the relationship between carbonate CO 2 -
3 and carbon dioxide CO 2 . Correspondence is not always well defined because there may be several ways to perform this formal dehydration, including combining two or more anions to make oligomers or polymers. Unlike neutralization, this formal dehydration sometimes produces fairly stable oxocarbons, such as the mellitic anhydride C 12 O 9 of the mellit C
12 O 6 -
12 through mellitic acid C 12 H 6 O 12
Hydrogenated Anion
For each oxocarbon anion C
x O n - y is principally n -1 partially hydrogenated anion with the formula H
k C
x O ( n - k ) -
y , where k ranges from 1 to n -1. This anion is generally indicated by the prefix "hydrogen" -, "dihydrogen" -, "trihydrogen" -, etc. But some of them have a special name: hydrogencarbonate HCO -
3 usually called bicarbonate, and hydrogenoxalate HC > 2 O -
4 is known as binoxalate.
Hydrogenated anions can be stable even if full protonated acids are not (as is bicarbonate).
Extreme case
Anion carbide, like acetylide C 2 - 2 and methanide C 4 - , can be seen as an extreme case of anion oxocarbon C
x O n -
y , with y equal to zero. The same can be said of oxygen anions just like oxide O 2 - , superoxide O -
2 , peroxide , 2 - 2 , and ozonide O -
3 .
List of oxocarbon anions
The following is a list of known or suspected oxocarbon anions
Several other oxocarbon anions have been detected in trace amounts, such as C
6 O -
6 , a single ionized rhodizonate version.
See also
- Oksocarbon
- Silicate
- Sodium percarbonate (actually carbonate perhidrate)
References
Source of the article : Wikipedia
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