The Concept of Functional Groups

The Concept of Functional Groups James Richard Fromm In organic chemistry, functional groups are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. Functional groups consist of one or more atoms, and they can be atoms of identical or different elements. The simplest organic molecule is one carbon bonded covalently to four hydrogens, CH 4. This compound, a gas, is called methane and is a major component of natural gas. The principle used is that organic compounds are named and generally understood as substituted compounds of carbon and hydrogen, the substitution being that of a functional group for one or more hydrogens. The simplest compounds of carbon and hydrogen are the Alkanes, followed by the Alkenes and Alkynes. The first carbon after the carbon that attaches to the functional group is called the alpha carbon. Functional groups are attached to the carbon backbone of organic molecules. They determine the characteristics and chemical reactivity of molecules. Functional groups are far less stable than the carbon backbone and are likely to participate in chemical reactions. Six common biological functional groups are hydrogen, hydroxyl, carboxyl, amino, phosphate, and methyl. -H

NH2CO2H

OP(OR)3

-CH3

Carboxy Amino Phosphate Methyl l The following is a list of common functional groups. In the formulas, the symbols R and R' usually denotes a hydrocarbon side chain of any length, but may sometimes refer to any group of atoms. Hydrogen

Hydroxyl

Haloalkanes (also known as Halogenoalkanes) are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, fluorine, chlorine, bromine or iodine, forming an organic halide. The most widely known family within this group are the chlorofluorocarbons (CFCs). The haloalkanes have the general formula R-X where R- represents some alkyl or aryl group and -X represents one of the members of the halogen family: fluorine, chlorine, bromine and/or iodine. R-X R-F R-Cl R-Br R-I Halogen FluoroChloroBromoIodoDerivatives An Alcohol functional group is a hydroxyl group bonded to an sp 3 hybridized carbon. It can be regarded as a derivative of water, with an alkyl group replacing one of the hydrogens. If an aryl group is present rather than an alkyl, the compound is generally called a phenol rather than an alcohol. Also, if the hydroxyl group is bonded to one of the sp2 hybridized carbons of an alkenyl group, the compound is referred to as an enol. The oxygen in an alcohol has a bond angle of around 109° (c.f. 104.5° in water), and two nonbonded electron pairs.

Alcohol Functional Group, Hydroxyl Ethanol, Ethyl Alcohol, Grain Alcohol Group An Aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom which is bonded to a hydrogen atom and double-bonded to an oxygen atom (chemical formula O=CH-), is called the aldehyde group. The aldehyde group is also called the aldo, formyl or methanoyl group. The word aldehyde seems to have arisen from alcoholdehydrogenated.

Aldehyde Functional Group, Aldo Methanal, Formaldehyde Group Ether is the general name for a class of chemical compounds which contain an oxygen atom connected to two (substituted) alkyl groups. A typical example is the solvent and anesthetic, diethyl ether, commonly referred to simply as "ether", (ethoxyethane, CH3-CH2-O-CH2-CH3).

Ether Functional Group Ethoxyethane, Diethyl Ether Ketones are either the functional group characterized by a carbonyl group (O=C) linked to two other carbon atoms or a compound that contains this functional group. A ketone can be generally represented by the formula: R1(CO)R2.

A carbonyl carbon bonded to two carbon atoms distinguishes ketones from carboxylic acids, aldehydes, esters, amides, and other oxygen -containing compounds. The double-bond of the carbonyl group distinguishes ketones from alcohols and ethers. The simplest ketone is acetone, dimethyl ketone or propanone.

Ketone Functional Group, Keto Group Propanone, Dimethyl Ketone, Acetone Carboxylic Acids are organic acids characterized by the presence of a carboxyl group, which has the formula -C(=O)OH, usually written -COOH or -CO2H. Carboxylic acids are Bronsted Acids — they are proton donors. Salts and anions of carboxylic acids are called carboxylates. The simplest series of carboxylic acids are the alkanoic acids, R-COOH, where R is a hydrogen or an alkyl group. Compounds may also have two or more carboxylic acid groups per molecule.

Carboxyl Functional Group Ethanoic Acid, Acetic Acid Esters are organic compounds in which an organic group from an alcohol (symbolized by R') replaces a hydrogen atom in the hydroxyl group of an organic acid. Organic acids are molecules which have an -OH group from which the hydrogen (H) can dissociate as an H+ ion. The most common esters are the carboxylate esters, where the acid in question is a carboxylic acid.

Ester Functional Group Isoamyl Ethanoate, Flavor of Banana Condensation reaction to form an ester is called esterification. Amines are organic compounds whose functional group contains nitrogen as the key atom. Structurally amines resemble ammonia, wherein one or more hydrogen atoms are replaced by organic substituents such as alkyl and aryl groups. An important exception to this rule is that compounds of the type RC(O)NR 2, where the C(O) refers to a carbonyl group, are called amides rather than amines. Amides and amines have different structures and properties, so the distinction is chemically important. Somewhat confusing is the fact that amines in which an N-H group has been replaced by an N-M group (M = metal) are also called amides. Thus (CH3)2NLi is lithium dimethylamide.

Amine Functional Group

Methamphetamine

An Amide o Amide Functional Group

or

Amide Functional Group

Nitroso refers to a functional group in organic chemistry which has the general formula R-N=O. Nitroso compounds can be prepared by the reduction of nitro compounds or by the oxidation of hydroxylamines. A good example is (CH3)3CNO, known formally as 2-methyl-2-nitrosopropane. R-N=O (CH3)3CNO Nitroso Functional Group 2-methyl-2-nitrosopropane Azo Compounds refer to chemical compounds bearing the functional group R-N=N-R', in which R and R' can be either alkyl or aryl. The N=N group is called an azo or diimide. R-N=N-R' 4hydroxyphenylazobenzene Many of the more stable derivatives contain two aryl groups due to the electron delocalization. The name azo comes from azote, an old name of nitrogen that originates in French and is derived from the Greek a (not) + zoe (to live). Nitro Compounds are organic compounds that contain one or more nitro functional groups (-NO2). They are often highly explosive; various impurities or improper handling can easily trigger a violent exothermic decomposition. Azo Functional Group

Aromatic nitro compounds are typically synthesized by the action of a mixture of nitric and sulfuric acids on a suitable organic molecule. Some examples of such compounds are trinitrophenol (picric acid) and trinitrotoluene (TNT). R-NO2 Nitro Functional Group A Nitrile is any organic compound which has a -C N functional group. In the -C N group, the carbon atom and the nitrogen atom are triple bonded together. The prefix cyano- is used in chemical nomenclature to indicate the presence of a nitrile group in a molecule. A cyanide ion is a negative ion with the formula CN-. The CN group is sometimes, less properly, referred to as a cyanide group orcyano group and compounds with them are sometimes referred to as cyanides. Nitriles sometimes release the highly toxic CN- cyanide ion. R-C N Nitrile Functional Group An Imine is a functional group or chemical compound containing a carbon-nitrogen double bond. Imines, due to their diverse reactivity, are common substrates in a wide variety of transformations. An imine can be synthesised by the nucleophilic addition of an amine to a ketone or aldehyde giving a hemiaminal -C(OH)(NHR)followed by an elimination of water to yield the imine. R2C=NR' Imine Functional Group The Cyanate ion is an anion consisting of one oxygen atom, one carbon atom, and one nitrogen atom, [OCN]-, in that order, and possesses 1 unit of negative charge, borne mainly by the nitrogen atom. The structure of cyanate can be considered to resonate. Cyanate Functional Group An Isocyanide (also called an Isonitrile is an organic compound with the functional group R-N C. The C N functionality is connected to the organic fragment via the nitrogen atom, not via carbon as is found in the isomeric nitriles, which have the connectivity R-CN. Hence the prefix iso. Nitrogen and carbon are connected through a triple bond with a positive charge on nitrogen and a negative charge on carbon.

Isocyanide/Isonitrile Functional Group Isocyanate is the functional group of atoms –N=C=O (1 nitrogen, 1 carbon, 1 oxygen), not to be confused with the cyanate functional group (see above). -N=C=O Isocyanate Functional Group Organic Peroxides are organic compounds containing the peroxide functional group (ROOR'). If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RC(O)OOR. The O-O bond easily breaks and forms free radicals of the form RO-. This makes organic peroxides useful as catalysts for some types of polymerization. R-O-O-R' Organic Peroxide Functional Group A Thiol/Mercaptan is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). Being the sulfur analogue of an alcohol group (-OH), this functional group is referred to either as a thiol group or a sulfhydryl group. Thiolate ions have the form R-S-. Such anions arise upon treatment of thiols with base.

Thiol or Mercaptan Functional Group A Thioether/Sulfide is a functional group that has the structure R1-S-R2. Like many other sulfur-containing compounds, volatile thioethers characteristically have foul odors. A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen. Because oxygen and sulfur belong to the chalcogens group in the periodic table, the chemical properties of ethers and thioethers share some commonalities. This functional group is important in biology, most notably in the amino acid methionine and the cofactor biotin. In organic chemistry , "Sulfide" usually refers to the linkage C-S-C, although the term thioether is less ambiguous. For example, the thioether dimethyl sulfide is CH3-S-CH3. Polyphenylene sulfide has the empirical formula C6H4S. Occasionally, the term sulfide refers to molecules containing the -SH functional group. For example, methyl sulfide can mean CH3-SH. The preferred descriptor for such SH-containing compounds is thiol or mercaptan, i.e. methanethiol or methyl mercaptan.

Thioether/Sulfide Functional Group

Disulfides - A disulfide bond is a single covalent bond derived from the coupling of thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore C-S-S-C. The terminology is almost exclusively used in biochemistry, bioinorganic and bioorganic chemistry. Formally the connection is called a persulfide, in analogy to a peroxide (R-O-O-R), but this terminology is rare. Three sulfur atoms singly bonded in a sequence are sometimes called a trisulfide bond, although there are in fact two S-S bonds. Disulfide bonds are usually formed from the oxidation of sulfhydryl (-SH) groups.

Disulfide Functional Group Sulfonic acids are a class of organic acids with the general formula RSO3H, where R is usually a hydrocarbon side chain. Sulfonic acids are typically much stronger acids than their carboxylic equivalents, and have the unique tendency to bind to proteins and carbohydrates tightly; most "washable" dyes are sulfonic acids (or have the functional sulfonyl group in them) for this reason. They are also used as catalysts and intermediates for a number of different products. Sulfonic acid salts (sulfonates) are important as detergents, and the antibacterial sulfa drugs are also sulfonic acid derivatives. The simplest example is methanesulfonic acid, CH3SO2OH, a reagent regularly used in organic chemistry. p-Toluenesulfonic acid is also an important reagent. Note that the sulfonic acids and sulfonates are analogous to carboxylic acids and carboxylates; in both cases, -C(=O)- is replaced by -S(=O)2-. Chemical properties are similar as well, although sulfonic acids are often even stronger acids than carboxylic acids, the hydrogen being easier to leave than in most compounds, and they readily form esters.

Sulfonic Acid Functional Group A Sulfoxide/Sulfinyl contains a sulfinyl functional group attached to two carbon atoms. The general structural formula is RS(O)R where R and R' are the organic groups. Sulfoxides can be considered as oxidized sulfides. A common sulfoxide is DMSO.

Sulfinyl Functional Alliin, an example of a sulfoxide occurring in nature. Group, RS(O)R A Sulfone/Sulfonyl contains a sulfonyl functional group attached to two carbon atoms. The central sulfur atom is twice double bonded to oxygen and has two further hydrocarbon substituents. The general structural formula is RS(O)2R where R and R' are the organic groups. A common sulfone is sulfolane C4H8SO2.

Sulfonyl Functional Group, RS(O)2R Phosphine is the common name for phosphorus hydride (PH3), also known by the IUPAC name phosphane and, occasionally, phosphamine. It is a colorless, flammable gas with a boiling point of -88 °C at standard pressure. Pure phosphine is odorless, but "technical grade" phosphine has a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphine (P2H4). Phosphines are also a group of substituted phosphines, with the structure R3P, where other functional groups replace hydrogens. They are important in catalysts where they complex to various metal ions. Phosphoranes are functional groups in chemistry with pentavalent phosphorus. It has the general structure PR5. The parent compound is the non-stable phosphoran PH5. Phosphate is also an organophosphorus compounds with the formula OP(OR) 3. Organophosphates are most commonly found in the form of adenosine phosphates, (AMP, ADP and ATP) and in DNA andRNA and can be released by the hydrolysis of ATP or ADP. Similar reactions exist for the other nucleoside diphosphates and triphosphates. Phosphoanhydride bonds in ADP and ATP, or other nucleoside diphosphates and triphosphates, contain high amounts of energy which give them their vital role in all living organisms. They are generally referred to as high energy phosphate, as are the phosphagens in muscle tissue. Compounds such as substituted phosphines, have uses in organic chemistry but do not seem to have any natural counterparts. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid.