Organic compounds of carbon

Carbonium ion (carbenium ion) is an organic ion with a positive charge on a carbon atom; i.e. it is an ion of the type R₃C⁺. Carbonium ions are intermediates in certain types of organic reaction (e.g. Williamson's synthesis). Certain fairly stable carbonium ions can be formed (carbocations). Carbonium ions can be prepared from an alkyl fluoride and a superacid, such as antimony pentafluoride (SbF₅) at low temperature. Carbonium atoms always have a strong affinity for such nucleophiles as water.

Carbanion is an organic ion with a negative charge on a carbon atom; i.e. it is an ion of the type R₃C^- . Carbanions are intermediates in certain types of organic reaction (e.g. the aldol reaction).

Carbonyl group is the group >C=O, found in aldehydes, ketones, carboxylic acids, amides. Carboxyl group is the organic group -COOH, present in carboxylic acids.

Carbonyl compound is a compound containing the carbonyl group >C=O. Aldehydes, ketones and carboxylic acids are examples of organic carbonyl compounds. Inorganic carbonyls are complexes in which carbon monoxide has coordinated to a metal atom or ion, as in nickel carbonyl, Ni(CO)_4.Carbonyl chloride (phosgene) is a colourless gas, COCl₂, with an odour of freshly cut hay. It is used in organic chemistry as a chlorinating agent and was formerly used as a war gas.

Carboxylic acids are organic compounds containing the group -COOH (the carboxyl group; i.e. a carbonyl group attached to a hydroxyl group). In systematic chemical nomenclature carboxylic-acid names end in the suffix -oic, e.g. ethanoic acid, CH₃COOH. They are generally weak acids. Many long-chain carboxylic acids occur naturally as esters in fats and oils and are therefore also known as fatty acids. Methanoic acid (formic acid) is a colourless pungent liquid, HCOOH; r.d. is 1.2; m.p. is 8°C; b.p. is 101°C. It can be made by the action of concentrated sulphuric acid on the sodium salt (sodium methanoate) and occurs naturally in ants and stinging nettles. Methanoic acid is the simplest of the carboxylic acids.

Carbene is a species of the type R₂C:, in which the carbon atom has two electrons that do not form bonds. Methylene, :CH₂, is the simplest example. Carbenes are highly reactive and exist only as transient intermediates in certain organic reactions. They attack double bonds to give cyclopropane derivatives. They also cause insertion reactions, in which the carbene group is inserted between the carbon and hydrogen atoms of a C-H bond:

C-H + :CR₂ ® C-CR₂-H.

Alcohols are organic compounds that contain the -OH group. In systematic chemical nomenclature alcohol names end in the suffix -ol. Examples are methanol, CH₃OH, and ethanol, C₂H₅OH. Primary alcoholshave two hydrogen atoms on the carbon joined to the -OH group (i.e. they contain the group -CH₂-OH). Secondary alcoholshave one hydrogen on this carbon (the other two bonds being to carbon atoms, as in (CH₃)₂CHOH). Tertiary alcoholshave no hydrogen on this carbon (as in(CH₃)₃ COH). The different types of alcohols may differ in the way they react chemically. For example, with potassium dichromate (VI) in sulphuric acid the following reactions occur:

primary alcohol ® aldehyde ® carboxylic acid

secondary alcohol® ketone

tertiary alcohol - no reaction.

Other characteristics of alcohols are reaction with acids to give esters and dehydration to give alkenes or ethers. Alcohols that have two -OH groups in their molecules are diols (ordihydric alcohols),those with three are triols(or trihydricalcohols). Methanol (methyl alcohol) is a colourless liquid, CH₃OH; r.d. is 0.79; m.p. is -93.9°C; b.p. is 64.96°C. It is made by catalytic oxidation of methane (from natural gas) using air. Methanol is used as a solvent and as a raw material for making methanal (mainly for urea-formaldehyde resins). It was formerly made by the dry distillation of wood (hence the name wood alcohol).

Aldehydes are organic compounds that contain the group -CHO (the aldehyde group; i.e. a carbonyl group (C=O) with a hydrogen atom bound to the carbon atom). In systematic chemical nomenclature, aldehyde names end with the suffix -al. Examples of aldehydes are methanal (formaldehyde), HCOH, and ethanal (acetaldehyde), CH₃CHO. Aldehydes are formed by oxidation of primary alcohols. Further oxidation yields carboxylic acids. They are reducing agents and tests for aldehydes include Fehling's test and Tollens reagent. Aldehydes have certain characteristic addition and condensation reactions. With sodium hydrogensulphate (IV) they form addition compounds of the type [RCOH(SO₃)H]^- Na⁺. Formerly these were known as bisulphite addition compounds.They also form addition compounds with hydrogen cyanide to give cyanohydrins and with alcohols to give acetals and undergo condensation reactions to yield oximes, hydrazones and semicarbazones. Aldehydes readily polymerize.

Methane is acolourless odourless gas, CH₄; m.p. is -182.5°C; b.p. is -164°C. Methane is the simplest hydrocarbon, being the first member of the alkane series. It is the main constituent of natural gas (-99%) and is an important raw material for producing other organic compounds. It can be converted into methanol by catalytic oxidation.

Benzene is a colourless liquid hydrocarbon, C₆H₆; r.d. is 0.88; m.p. is 5.5°C; b.p. is 80.1°C. It is now made from gasoline and from petroleum by catalytic reforming (formerly obtained from coal tar). Benzene is the archetypal aromatic compound. It has an unsaturated molecule, yet will not readily undergo addition reactions. On the other hand, it does undergo substitution reactions in which hydrogen atoms are replaced by other atoms or groups. This behaviour occurs because of delocalization of p-electrons over the benzene ring and all the C-C bonds in benzene are equivalent and intermediate in length between single and double bonds. It can be regarded as a resonance hybrid of Kekule and Dewar structures. In formulae it can be represented by a hexagon with a ring inside it.

Texts from scientific articles

Journal: Biomaterials

Mesoporous carbide-derived carbon with porosity tuned

for efficient adsorption of cytokines

<== попередня сторінка	\|	наступна сторінка ==>
Inorganic compounds of carbon	\|	Abstract

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