There are more carbon compounds than for any other element except hydrogen. The majority of these molecules are organic carbon compounds (e.g., benzene, sucrose), although a large number of inorganic carbon compounds also exist (e.g., carbon dioxide).
One important characteristic of carbon is catenation, which is the ability to form long chains or polymers. These chains may be linear or can form rings. Carbon is very reactive.
It forms a huge number of compounds with many other elements. Compounds containing carbon outnumber the compounds of all the other elements.
Carbon is known to form a number of compounds due to the salient properties it carries with itself. The most general or the basic compound formed by carbon is methane (CH4).
Such types of compounds formed by the combination of hydrogen and carbon are known as hydrocarbons. You can easily guess the molecular formula of such types of compounds by just adding hydrogen to satisfy the valency of carbon atoms.
Ethane which has two carbon atoms will need six hydrogen atoms to satisfy the valency of each carbon atom (keeping in mind the single bond existing between both the carbon atoms).
Hence, the molecular formula for ethane is C2H6. Now, the bond between two or more carbon atoms involved in the formation of a compound can be a single, double or even a triple bond.
Carbon is present as carbon dioxide in Earth’s atmosphere at a concentration of about 0.04 percent by volume, an amount that is increasing.
The Carbon dioxide is a greenhouse gas, and it is dissolved in all natural waters. Carbon occurs in the crust of Earth in the form of carbonates in such rocks as marble, limestone, and chalk and in hydrocarbons—the principal constituents of coal, petroleum, and natural gas.
Carbonate minerals are important sources of various metals, such as sodium, magnesium, calcium, copper, and lead. At ordinary temperatures, carbon is very unreactive—it is difficult to oxidize and does not react with acids or alkalies.
At high temperatures, it combines with sulfur vapour to form carbon disulfide, with silicon and certain metals to form carbides, and with oxygen to form oxides.
The most important are carbon monoxide, CO, and carbon dioxide, CO2. Because carbon combines readily with oxygen at high temperatures that are present in compounds with metals, large quantities of coke (an inexpensive form of carbon) are used in metallurgical processes to reduce (remove oxygen from) metal oxide ores as those of iron and zinc.
Abundance of Carbon Compounds
More than one million carbon compounds have been described in the chemical literature, and chemists synthesize many new ones each year.
Much of the diversity and complexity of organic forms is due to the capacity of carbon atoms to bond with one another in the various chain and ring structures and three-dimensional conformations and link with other atoms.
This derives its name from the fact that in the 19th century, most of the then-known carbon compounds were considered to have originated in living organisms.
All organic compounds, such as proteins, carbohydrates, and fats, contain carbon, and all plant and animal cells consist of carbon compounds and their polymers. (Polymers are macromolecules consisting of many simple molecules bonded together in specific ways.)
With hydrogen, oxygen, nitrogen, and a few other elements, carbon forms a compound that makeup about 18 percent of all the matter in living things. The processes by which organisms consume carbon and return it to their surroundings constitute the carbon cycle.
Reactions of Carbon Compounds
A type of chemical reaction in which one substance (an oxidizing agent) accepts electrons from another substance (a reducing agent) and is thereby reduced (while the reducing agent is oxidized) is frequently observed with carbon and its compounds.
Although carbon is usually a reducing agent, elemental carbon is a moderately strong oxidizing agent under acidic conditions. The large energy of the carbon-carbon bond makes activation energy requirements for the reaction so high that direct reduction of carbon—e.g., to methane (formula CH4)—is impractical.
Reduction of carbon monoxide to elemental carbon and oxidation of carbon monoxide to carbon dioxide are both feasible but impractical in solution.
Under alkaline conditions, only the oxidation of formate ion (HCO2- ) to carbonate ion (CO32- ) is reasonable. Carbon monoxide (CO) is both more readily absorbed and more firmly bound to the haemoglobin of the blood than is oxygen and is thus, even in small concentrations, a dangerous asphyxiant.
However, carbon dioxide (CO2) is an asphyxiant of significance only in relatively large concentrations; in small concentrations, it stimulates breathing. Hydrogen cyanide (HCN) and its derivatives (cyanogen compounds, cyanides) are toxic as protoplasmic poisons through the inhibition of tissue oxidation.
Carbon tetrachloride (CCl4) and other chlorinated hydrocarbons damage the nervous system. The most toxic organic compounds are derivatives that contain the halogen elements (fluorine, chlorine, bromine, and iodine), sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic lead, and mercury.
Most organometallic compounds are toxic, while oxygen-containing derivatives of the hydrocarbons are usually less toxic.
Properties of Carbon Compounds
- Most carbon compounds have low reactivity at ordinary temperature but may react vigorously when heat is applied. For example, cellulose in wood is stable at room temperature, yet burns when heated.
- As a consequence, organic carbon compounds are considered combustible and may be used as fuels. Examples include tar, plant matter, natural gas, oil, and coal. Following combustion, the residue is primarily elemental carbon.
- Many carbon compounds are nonpolar and exhibit low solubility in water. For this reason, water alone is not sufficient to remove oil or grease.
- Compounds of carbon and nitrogen often make good explosives. The bonds between the atoms may be unstable and likely to release considerable energy when broken.
- Compounds containing carbon and nitrogen typically have a distinct and unpleasant odor as liquids. The solid form may be odorless. An example is nylon, which smells until it polymerizes.
Existence of Carbon Compounds
Carbon is one of the more widespread heavy elements – it may make up almost 0.5 percent of the universe mass. The solar system formed from a material that was quite rich in carbon.
Even then the element only makes up 0.025 percent of Earth’s crust and most of this carbon bound up in rocks and minerals such as limestone and chalk.
But carbon is highly concentrated in living creatures and accounts for nearly one-quarter of atoms in our tissues.
The carbon compounds exist mainly in three ways :
In such kind of arrangement one carbon atom is bonded to another carbon forming a straight line without developing any branches. Low molecular weight hydrocarbons exist in straight chains. For example ethane.
Carbon compounds with higher molecular weight mostly exist in branched form i.e. one of the carbon atoms is bonded to more than two carbon atoms. For example isopentane.
In this kind of arrangement, three or more carbon atoms are linked together in such a way that they form closed cycles. Such compounds are also known as cyclic compounds. For example, cyclohexane.
Chemical Bonds Formed by Carbon
Carbon most often forms covalent bonds with other atoms. Carbon forms nonpolar covalent bonds when it bonds to other carbon atoms and polar covalent bonds with nonmetals and metalloids. In some instances, carbon forms ionic bonds.
An example is a bond between calcium and carbon in calcium carbide, CaC2. Carbon is usually tetravalent (oxidation state of +4 or -4).
However, other oxidation states are known, including +3, +2, +1, 0, -1, -2, and -3. Carbon has even been known to form six bonds, as in hexamethyl benzene.
Thus, based on the number of bonds between the C–atoms involved in forming a compound, we classify carbon compounds into two major categories: saturated and unsaturated carbon compounds.
Types of Carbon Compounds
Followings are the types of carbon compounds
Saturated Carbon Compounds
These are the compounds in which various carbon atoms in a chain or a ring are linked together by single bonds only. Alkanes are the most common examples of saturated chain carbon compounds.
Unsaturated Carbon Compounds
These are the compounds in which various carbon atoms in a chain or a ring are linked together by double or triple bonds.
Alkenes (where carbon atoms are linked through double bonds) and alkynes (where carbon atoms are linked through triple bonds) are the most common examples of unsaturated chain carbon compounds.
Although the two main ways to classify carbon compounds are as organic or inorganic, there are so many different compounds that they can be further subdivided
Allotropes are different forms of an element. Technically, they are not compounds, although that name often calls the structures.
Important allotropes of carbon include amorphous carbon, diamond, graphite, graphene, and fullerenes. Other allotropes are known. Even though allotropes are all forms of the same element, they have vastly different properties from each other.
The known inorganic chemistry of the allotropes of carbon (diamond, graphite, and the fullerenes) blossomed with the discovery of buckminsterfullerene in 1985 as additional fullerenes and their various derivatives were discovered.
One such class of derivatives is inclusion compounds, in which the all-carbon shell of the fullerene encloses an ion. This inclusion is denoted by the “@” symbol in endohedral fullerenes.
For example, an ion consisting of a lithium-ion trapped within buckminsterfullerene would be denoted [email protected] As with any other ionic compound, this complex ion could, in principle, pair with a counterion to form a salt. Other elements are also incorporated in so-called graphite intercalation compounds.
Organic compounds were once defined as any carbon compound formed exclusively by a living organism. Many of these compounds can be synthesized in a lab or have been found distinct from organisms, so the definition has been revised (although not agreed upon).
An organic compound must contain at least carbon. Most chemists agree hydrogen must also be present. Even so, the classification of some compounds is disputed.
Major classes of organic compounds include (but are not limited to) carbohydrates, lipids, proteins, and nucleic acids. Examples of organic compounds include benzene, toluene, sucrose, and heptane.
Read full article on Organic Compounds- Organic Compounds
Inorganic compounds may be found in minerals and other natural sources or may be made in the lab.
Examples include carbon oxides (CO and CO2), carbonates (e.g., CaCO3), oxalates (e.g., BaC2O4), carbon sulfides (e.g., carbon disulfide, CS2), carbon-nitrogen compounds (e.g., hydrogen cyanide, HCN), carbon halides, and carboranes.
Read full article on Inorganic Compounds – Inorganic Compounds
There are many oxides of carbon (oxocarbons), of which the most common are carbon dioxide (CO2) and carbon monoxide (CO).
Other less known oxides include carbon suboxide (C3O2) and mellitic anhydride (C12O9).There are also numerous unstable or elusive oxides, such as dicarbon monoxide (C2O), oxalic anhydride (C2O4), and carbon trioxide (CO3).
Important inorganic carbon-sulfur compounds are the carbon sulfides carbon disulfide (CS2) and carbonyl sulfide (OCS). Carbon monosulfide (CS) unlike carbon monoxide is very unstable. Important compound classes are thiocarbonates, thiocarbamates, dithiocarbamates and trithiocarbonates.
Small inorganic carbon-nitrogen compounds are cyanogen, hydrogen cyanide, cyanamide, isocyanic acid and cyanogen chloride. Paracyanogen is the polymerization product of cyanogen. Cyanuric chloride is the trimer of cyanogen chloride, and 2-cyanoguanidine is the dimer of cyanamide.
Other inorganic compounds include the inorganic salts and complexes of the carbon-containing cyanide, cyanate, fulminate, thiocyanate and cyanamide ions.
Examples of cyanides are copper cyanide (CuCN) and potassium cyanide (KCN). Examples of cyanates are potassium cyanate (KNCO) and silver cyanate (AgNCO), examples of fulminates are silver fulminate (AgOCN) and mercury fulminate (HgOCN), and an example of thiocyanate is potassium thiocyanate (KSCN)
Organometallic compound contain at least one carbon-metal bond. Examples include tetraethyl lead, ferrocene, and Zeise’s salt.
Organometallic Compounds are chemical compounds that contain at least one bond between a metallic element and a carbon atom belonging to an organic molecule.
Even metalloid elements such as silicon, tin, and boron are known to form organometallic compounds used in some industrial chemical reactions.
The catalysis of reactions wherein the target molecules are polymers or pharmaceuticals can be done with the help of organometallic compounds, increasing the rate of the reactions.
Generally, the bond between the metal atom and the carbon belonging to the organic compound is covalent. When metals with relatively high electropositivity (such as sodium and lithium) form these compounds, a carbanionic nature is exhibited by the carbon, which is bound to the central metal atom.
An example of an organometallic compound wherein carbons belonging to a benzene molecule bond with chromium is illustrated above.
A few more examples of these compounds are Grignard reagents, tetracarbonyl nickel, and dimethyl magnesium.
Pure metals are smelted, in which coke is used as a fuel and reducing agent. This leads to many alloys having an element of carbon in them. Carbon steel is one such example where iron is alloyed with carbon.
All alcoholic beverages in the world are a form of carbon compounds. Alcoholic beverages are made by adding Ethanol.
The process of fermentation is used to produce ethanol (alcohol) from glucose. One molecule of glucose gives Ethanol and carbon dioxide as by-products. So alcohols contain carbohydrates.
Names of Carbon Compounds
Certain classes of compounds have names that indicate their composition :
- Carbides: Carbides are binary compounds formed by carbon and another element with a lower electronegativity. Examples include Al4C3, CaC2, SiC, TiC, WC.
- Carbon Halides: Carbon halides consist of carbon bonded to a halogen. Examples include carbon tetrachloride (CCl4) and carbon tetraiodide (CI4).
- Carboranes: Carboranes are molecular clusters that contain both carbon and boron atoms. An example is H2C2B10H10.
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