A functional group is a group of atoms in a molecule with distinctivechemical properties, regardless of the otheratoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule bycovalent bonds. For repeating units ofpolymers, functional groups attach to theirnonpolar core ofcarbon atoms and thus add chemical character to carbon chains. Functional groups can also becharged, e.g. incarboxylate salts (−COO−), which turns the molecule into apolyatomic ion or acomplex ion. Functional groups binding to a central atom in acoordination complex are calledligands. Complexation andsolvation are also caused by specific interactions of functional groups. In the common rule of thumb "like dissolves like", it is the shared or mutually well-interacting functional groups which give rise tosolubility. For example,sugar dissolves in water because both share thehydroxyl functional group (−OH) and hydroxyls interact strongly with each other. Plus, when functional groups are moreelectronegative than atoms they attach to, the functional groups will become polar, and the otherwise nonpolar molecules containing these functional groups become polar and so become soluble in someaqueous environment.
Combining the names of functional groups with the names of the parentalkanes generates what is termed asystematic nomenclature for namingorganic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the functional group is called thealpha carbon; the second, beta carbon, the third, gamma carbon, etc. If there is another functional group at a carbon, it may be named with the Greek letter, e.g., the gamma-amine ingamma-aminobutyric acid is on the third carbon of the carbon chain attached to the carboxylic acid group.IUPAC conventions call for numeric labeling of the position, e.g. 4-aminobutanoic acid. In traditional names various qualifiers are used to labelisomers, for example, isopropanol (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). The termmoiety has some overlap with the term "functional group". However, a moiety is an entire "half" of a molecule, which can be not only a single functional group, but also a larger unit consisting of multiple functional groups. For example, an "aryl moiety" may be any group containing anaromatic ring, regardless of how many functional groups the said aryl has.
The following is a list of common functional groups.[3] In the formulas, the symbols R and R' usually denote an attached hydrogen, or ahydrocarbonside chain of any length, but may sometimes refer to any group of atoms.
Hydrocarbons are a class of molecule that is defined by functional groups calledhydrocarbyls that contain only carbon and hydrogen, but vary in the number and order of double bonds. Each one differs in type (and scope) of reactivity.
Haloalkanes are a class of molecule that is defined by a carbon–halogen bond. This bond can be relatively weak (in the case of an iodoalkane) or quite stable (as in the case of a fluoroalkane). In general, with the exception offluorinated compounds, haloalkanes readily undergonucleophilic substitution reactions orelimination reactions. The substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity.
Compounds that contain C–O bonds each possess differing reactivity based upon the location andhybridization of the C–O bond, owing to the electron-withdrawing effect of sp-hybridized oxygen (carbonyl groups) and the donating effects of sp2-hybridized oxygen (alcohol groups).
Compounds that contain sulfur exhibit unique chemistry due to sulfur's ability to form more bonds than oxygen, its lighter analogue on the periodic table. Substitutive nomenclature (marked as prefix in table) is preferred over functional class nomenclature (marked as suffix in table) for sulfides, disulfides, sulfoxides and sulfones.
Compounds that contain phosphorus exhibit unique chemistry due to the ability of phosphorus to form more bonds than nitrogen, its lighter analogue on the periodic table.
These names are used to refer to the moieties themselves or to radical species, and also to form the names of halides and substituents in larger molecules.
When the parent hydrocarbon is unsaturated, the suffix ("-yl", "-ylidene", or "-ylidyne") replaces "-ane" (e.g. "ethane" becomes "ethyl"); otherwise, the suffix replaces only the final "-e" (e.g. "ethyne" becomes "ethynyl").[4]
When used to refer to moieties, multiple single bonds differ from a single multiple bond. For example, amethylene bridge (methanediyl) has two single bonds, whereas amethylidene group (methylidene) has one double bond. Suffixes can be combined, as in methylidyne (triple bond) vs. methylylidene (single bond and double bond) vs. methanetriyl (three double bonds).
There are some retained names, such asmethylene for methanediyl, 1,x-phenylene for phenyl-1,x-diyl (where x is 2, 3, or 4),[5]carbyne for methylidyne, andtrityl for triphenylmethyl.
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