chemical nomenclature

Chemistry

2022

We explain what the chemical nomenclature is and its different types. Also, the nomenclatures in organic and inorganic chemistry.

The chemical nomenclature names, organizes and classifies the various chemical compounds.

What is the chemical nomenclature?

In chemistry It is known as nomenclature (or chemical nomenclature) to the set of rules and formulas that determine the way to name and represent the various chemical compounds known to the human being, depending on the elements that compose them and the proportion in each element.

The importance of chemical nomenclature lies in the possibility of naming, organizing and classifying the various types of chemical compounds, in such a way that only with their identifying term it is possible to have an idea of ​​what type of elements compose them and, therefore, what type of reactions can be expected from these compounds.

There are three chemical nomenclature systems:

  • Stoichiometric or systematic system (recommended by the IUPAC). Name the compounds based on the number of atoms of each element that make them up. For example: The compound Ni2O3 is called dinickel trioxide.
  • Functional, classic or traditional system. It uses various suffixes and prefixes (such as -oso, -ico, hypo-, per-) depending on the Valencia atomic element of the compound. This naming system is largely out of use. For example: The compound Ni2O3 is called nickel oxide.
  • STOCK system. In this system the name of the compound Includes in Roman numerals (and sometimes as a subscript) the valence of the atoms present in the compound molecule. For example: The compound Ni2O3 is called oxide nickel (III).

On the other hand, the chemical nomenclature varies depending on whether it is organic compounds or inorganic.

Nomenclature in organic chemistry

Aromatic hydrocarbons can be monocyclic or polycyclic.

Before talking about the nomenclature of the different types of organic compounds, it is necessary to define the term “locator”. The locator is the number used to indicate the position of an atom in a hydrocarbon chain or cycle. For example, in the case of pentane (C5H12) and cyclopentane (C5H10), each carbon atom is listed as shown in the following figure:

On the other hand, it is convenient to mention the tetravalence of carbon, which means that this element has 4 valences, therefore, it can form only 4 bonds with a wide combination of them. That explains the reason why in each organic compound we will almost never see or put a carbon atom with more than 4 bonds.

In organic chemistry there are mainly two nomenclature systems:

  • Substitute nomenclature. A hydrogen of the hydrocarbon structure is replaced by the corresponding functional group. Depending on whether the functional group acts as a substituent or as a main function, it will be named as a prefix or suffix of the name of the hydrocarbon. For example:
    • Principal function. A hydrogen on carbon 3 of pentane is replaced by the group -OH (-ol). It is named: 3-pentanol.
    • Substituent. A hydrogen of carbon 1 of pentane is replaced by the group -Cl (chloro-), it is named, 1-chloropentane. If a hydrogen of carbon 2 is substituted, it is named, 2-chloropentane.

Clarification: The hydrogens in the above structures are implied for simplicity. Each union between two lines means that there is a carbon atom with its corresponding hydrogens, always respecting tetravalence.

  • Radical-function nomenclature. The name of the radical corresponding to the hydrocarbon is put as suffix or prefix of the functional group name. In the case of being a functional group of the main function type, it would be, for example, pentylamine or 2-pentylamine. In case of being a substituent type functional group, it would be, for example, pentyl chloride (it can be seen that it is the same structure as 1-chloropentane but using another nomenclature to name it).

    Prefix Functional group Prefix Functional group
    -F fluoro- -NO2 nitro-
    -Cl chlorine- -OR R-oxy-
    -Br bromine- -NO nitrous-
    -I iodine- -N3 azido-

    Table 1: Very common substituent names.

    Table 2: Very common organic radical names.

Hydrocarbon nomenclature

Hydrocarbons are compounds made up of carbon (C) and hydrogen (H) atoms. They are classified into:

  • Aliphatic hydrocarbons. They are non-aromatic compounds. If their structure closes and forms a cycle, they are called alicyclic compounds. For example:
    • Alkanes They are compounds of an acyclic nature (that do not form cycles) and saturated (all their carbon atoms are linked to each other with covalent bonds simple). They respond to the general formula CnH2n + 2, where n represents the number of carbon atoms. In all cases the suffix -ano is used to name them. They may be:
      • Linear alkanes. They have a linear chain. To name them, the suffix -ano will be combined with the prefix that denotes the number of carbon atoms present. For example, hexane has 6 carbon atoms (hex-) (C6H14). Some examples are shown in Table 3.

        Name Amount of carbons Name Amount of carbons
        methane 1 heptane 7
        ethane 2 octane 8
        propane 3 nonano 9
        butane 4 dean 10
        pentane 5 undecane 11
        hexane 6 dodecane 12

        Table 3: Names of alkanes according to the amount of carbon atoms that their structure contains.

      • Branched alkanes. If they are not linear but branched, the longest hydrocarbon chain with the most branches (the main chain) must be found, its carbon atoms are counted from the end closest to the branch and the branches are named indicating their position in the chain main (as we saw with the locator), replacing the suffix -ano with -il (see Table 2) and adding the corresponding numeric prefixes in case there are two or more equal strings. The main chain is chosen so that it has the smallest possible combination of locators. Finally the main chain is named normally. For example, 5-ethyl-2-methylheptane has a heptane backbone (hep-, 7 carbon atoms) with a methyl radical (CH3-) on the second carbon atom and an ethyl radical (C2H5-) on the fifth. . This is the smallest possible combination of branch positions for this compound.
      • Alkane radicals (produced by losing a hydrogen atom attached to one of its carbons). They are named by substituting the suffix -ano for -ilo and indicating it with a hyphen in the Chemical bond For example, from methane (CH4) the methyl radical (CH3-) is obtained. (See Table 2). It should be clarified that, for nomenclature, the ending -il can also be used for radicals when they act as substituents. For example:
    • Cycloalkanes. They are alicyclic compounds that respond to the general formula CnH2n. They are named after the linear alkanes but adding the prefix cyclo- to the name, for example, cyclobutane, cyclopropane, 3-isopropyl-1-methyl-cyclopentane. In these cases, the smallest possible combination of the numbers of the atoms that have substituents should also be chosen. For example:
    • Alkenes and alkynes. They are unsaturated hydrocarbons, since they have a double (alkenes) or triple (alkynes) carbon-carbon bond. They respond, respectively, to formulas general CnH2n and CnH2n-2. They are named similarly to alkanes, but different rules apply to them based on the location of their multiple bonds:
      • When there is a carbon-carbon double bond, the suffix -ene is used (instead of -ane as in alkanes) and the respective number prefixes are added if the compound has more than one double bond, for example -diene, -triene, -tetraene.
      • When there is a carbon-carbon triple bond, the suffix -ino is used and the respective number prefixes are added if the compound has more than one triple bond, eg, -diino, -triino, -tetraino.
      • When there are carbon-carbon double and triple bonds, the suffix -enino is used and the respective number prefixes are added if there are several of these multiple bonds, for example, -dienino, -trienino, -tetraenino.
      • The location of the multiple bond is indicated by the number of the first carbon of that bond.
      • If there are branches, the longest chain with the greatest number of double or triple bonds is chosen as the main chain. The chain is chosen looking for the location of the double or triple bond to be as small as possible.
      • Organic radicals that come from alkenes are named by substituting the suffix -eno for -enyl (if it acts as a substituent, -enyl) and radicals coming from alkynes are substituted -ino for -inyl (if it acts as a substituent, -inyl).
        Compound Substituent Compound Substituent
        ethene ethenyl ethyne ethinyl
        propene propenyl tip propynyl
        butene butenyl butino butynyl
        pentene pentenyl pentine pentynyl
        hexene hexenyl hexine hexinyl
        heptene heptenyl heptin heptinyl
        octene octenyl october octinyl

        Table 4: Names of substituent radicals of alkenes and alkynes.


  • Aromatic hydrocarbons. They are known as arenos. They are conjugated cyclic compounds (alternating a single bond and a multiple bond in their structure). They have rings of flat structures and very stable due to conjugation. Many include benzene (C6H6) and its derivatives, although there are numerous other varieties of aromatic compounds. They can be classified into:
    • Monocyclic. They are named from derivations of the name of benzene (or some other aromatic compound), listing its substituents with numerator prefixes (locators). If the aromatic ring has several substituents, they are named in alphabetical order, always looking for the smallest possible combination of locators. If any substituent involves a ring, this is put in position one in the aromatic ring, and it continues to be named according to the alphabetical order of the rest of the substituents. On the other hand, the radical of the benzene ring is called phenyl (if it acts as a substituent, -phenyl). For example:

      Another way to define the position of the substituents in aromatic hydrocarbons is by using the ortho, meta and para nomenclature. This consists of locating the position of other substituents based on the position of an initial substituent, for example:
    • Polycyclic. They are mostly named by their generic name, since they are very specific compounds. But the suffix -eno or -enyl can also be used for them. These polycycles can be formed by several fused aromatic rings, or connected by C-C bonds. In these compounds, the locators are usually put with numbers for the main structure (the one with the most cycles) and with numbers with "premiums" for the secondary structure. For example:
  • Alcohols. Alcohols are organic compounds that contain a hydroxyl group (-OH).Their structure is formed by substituting an H for the group -OH in a hydrocarbon, therefore, they are defined by the general formula R-OH, where R is any hydrocarbon chain. They are named using the suffix -ol instead of the ending -o of the corresponding hydrocarbon. If the group -OH acts as a substituent, then it is named hydroxy-. If a compound has several hydroxyl groups, it is called a polyol or polyol, and it is named by numbering prefixes.
  • Phenols Phenols are similar to alcohols, but have the hydroxyl group attached to an aromatic benzene ring, rather than a linear hydrocarbon. They respond to the formula Ar-OH. To name them, the suffix -ol is also used together with that of the aromatic hydrocarbon. Some examples of alcohols and phenols are:
  • Ethers The ethers are governed by the general formula R-O-R ', where the radicals at the ends (R- and R'-) can be identical or different groups from the alkyl or aryl group. Ethers are named after the end of each alkyl or aryl group in alphabetical order, followed by the word "ether." For example:
  • Amines They are organic compounds derived from ammonia by substitution of one or some of its hydrogens by radical alkyl or aryl groups, obtaining aliphatic amines and aromatic amines respectively. In both cases they are named using the suffix -amine or the general name is preserved. For example:
  • Carboxylic acids. They are organic compounds that have a carboxyl group (-COOH) as part of their structure. This functional group is composed of a hydroxyl group (-OH) and a carbonyl group (-C = O). To name them, the chain with the highest number of carbons that contains the carboxyl group is considered as the main chain. Then it is used as ending -ico or -oico to name them. For example:
  • Aldehydes and ketones. They are organic compounds that have a carbonyl functional group. If the carbonyl is found at one end of the hydrocarbon chain we will speak of an aldehyde, and it will in turn be linked to a hydrogen and an alkyl or aryl group. We will speak of ketones when the carbonyl is within the hydrocarbon chain and linked through the carbon atom to alkyl or aryl groups on both sides. To name aldehydes, the suffix -al is used at the end of the name of the compound, following the same numbering rules according to the number of atoms. They can also be named using the general name of the carboxylic acid they come from, and changing the suffix -ico to -aldehyde. For example:

    To name ketones, the suffix -one is used at the end of the name of the compound, following the same numbering rules according to the number of atoms. You can also name the two radicals attached to the carbonyl group followed by the word ketone. For example:
  • Esters They should not be confused with ethers, since they are acids whose hydrogen is replaced by an alkyl or aryl radical. They are named by changing the suffix -ico of the acid by -ate, followed by the name of the radical that replaces the hydrogen, without the word “acid”. For example:
  • Amides They should not be confused with amines. They are organic compounds that are produced by substituting the -OH group of a reference acid for the -NH2 group. They are named by substituting -amide for the -ico end of the reference acid. For example:
  • Acid halides. They are organic compounds derived from a carboxylic acid in which the -OH group is replaced by an atom of a halogen element. They are named by substituting -yl for the suffix -ico and the word "acid" for the name of the halide. For example:
  • Acid anhydrides. They are organic compounds derived from carboxylic acids. They can be symmetrical or asymmetrical. If they are symmetrical, they are named substituting the word acid for "anhydride". For example: acetic anhydride (from acetic acid). If they are not, both acids are combined and preceded by the word “anhydride”. For example:
  • Nitriles. They are organic compounds that have the functional group -CN. In this case the -ico termination of the reference acid is replaced by -nitrile. For example:

Nomenclature in inorganic chemistry

Salts are the product of the union of acidic and basic substances.
  • Oxides. They are compounds that are formed with oxygen and some other metallic element or non metallic. They are named using prefixes according to the number of atoms that each oxide molecule has. For example: digalium trioxide (Ga2O3), carbon monoxide (CO). When the oxidized element is metallic, they are called basic oxides; when it is non-metallic, they are called acid anhydrides or oxides. In general, oxygen in oxides has an oxidation state of -2.
  • Peroxides They are compounds formed by the combination of the peroxo group (-O-O-) O2-2 and another chemical element. Generally, oxygen has oxidation state -1 in the peroxo group. They are named the same as oxides but with the word "peroxide". For example: calcium peroxide (CaO2), dihydrogen peroxide (H2O2).
  • Superoxides They are also known as hyperoxides. Oxygen has a -½ oxidation state in these compounds. They are regularly named after oxides, but using the word "hyperoxide" or "superoxide." For example: potassium superoxide or hyperoxide (KO2).
  • Hydrides They are compounds formed by hydrogen and another element. When the other element is metallic, they are called metallic hydrides and when it is not metallic they are called non-metallic hydrides. Its nomenclature depends on the metallic or non-metallic nature of the other element, although in some cases the common names are used, as in ammonia (or nitrogen trihydride).
    • Metal hydrides. To name them, the numerical prefix is ​​used according to the number of hydrogen atoms followed by the term "hydride". For example: potassium monohydride (KH), lead tetrahydride (PbH4).
    • Non-metallic hydrides. The ending -ide is added to the non-metallic element and then the phrase "hydrogen" is added. They are usually found in gaseous state. For example: hydrogen fluoride (HF (g)), dihydrogen selenide (H2Se (g)).
  • Oxacids. They are compounds that are also called oxoacids or oxyacids (and popularly "acids"). They are acids that contain oxygen. Its nomenclature requires the use of the prefix corresponding to the number of oxygen atoms, followed by the word "oxo" attached to the name of the nonmetal ending in "-ate". At the end the phrase "hydrogen" is added. For example: hydrogen tetraoxosulfate or sulfuric acid (H2SO4), hydrogen dioxosulfate or hyposulfurous acid (H2SO2).
  • Hydracids. They are compounds formed by hydrogen and a nonmetal. By dissolving them in Water they give acidic solutions. They are named using the prefix “acid” followed by the name of the non-metal, but with the ending “hydric”. For example: hydrofluoric acid (HF (aq)), hydrochloric acid (HCl (aq)), hydrogen sulfide (H2S (aq)), selehydric acid (H2Se (aq)). Whenever the formula of a hydracid is represented, it must be clarified that it is in aqueous solution (aq) (otherwise, it can be confused with a non-metallic hydride).
  • Hydroxides or bases. They are compounds formed by the union of a basic oxide and water. They are recognized by the functional group -OH. They are generically named as hydroxide, attached to the respective prefixes depending on the amount of hydroxyl groups present. For example: lead dihydroxide or lead (II) hydroxide (Pb (OH) 2), lithium (LiOH).
  • You go out. Salts are the product of the union of acidic and basic substances. They are named according to their classification: neutral, acidic, basic and mixed.
    • Neutral salts. They are formed by the reaction between an acid and a base or hydroxide, releasing water in the process. They can be binary and ternary depending on whether the acid is a hydracid or an oxacid.
      • If the acid is a hydracid, they are called haloid salts. They are named using the suffix -uro on the non-metallic element, and the prefix corresponding to the amount of this element. For example: sodium chloride (NaCl), iron trichloride (FeCl3).
      • If the acid is an oxacid, they are also called oxysalts or ternary salts. They are named using the numerical prefix according to the amount of "oxo" groups (amount of oxygen O2-), and the suffix -ate in the nonmetal, followed by the oxidation state of the nonmetal written in Roman numerals and in parentheses. They can also be named using the name of the anion followed by the name of the metal. For example: calcium tetraoxosulfate (VI) (Ca2 +, S6 +, O2-) or calcium sulfate (Ca2 +, (SO4) 2-) (CaSO4), sodium tetraoxyphosphate (V) (Na1 +, P5 +, O2-) or phosphate sodium (Na1 +, (PO4) 3-) (Na3PO4).
    • Acid salts. They are formed by the replacement of hydrogen in an acid by metal atoms. Its nomenclature is the same as that of the ternary neutral salts, but adding the word “hydrogen”. For example: sodium hydrogen sulfate (VI) (NaHSO4), a hydrogen from sulfuric acid (H2SO4) is exchanged for a sodium atom, potassium hydrogen carbonate (KHCO3), a hydrogen from carbonic acid (H2CO3) is exchanged for an atom of potassium.
    • Basic salts. They are formed by replacing the hydroxyl groups of a base with the anions of an acid. Its nomenclature depends on or an oxacid.
      • If the acid is a hydracid, the name of the nonmetal with the suffix -ide is used and the prefix of the number of -OH groups is prepended, followed by the term “hydroxy”. At the end the oxidation state of the metal is set if necessary. For example: FeCl (OH) 2 would be iron (III) dihydroxychloride.
      • If the acid is an oxacid, the term "hydroxy" is used with its corresponding prefix number. Then the suffix corresponding to the number of "oxo" groups is added and the termination -ate is added to the nonmetal, followed by its oxidation state written in Roman numerals and in parentheses. Finally, the name of the metal is put followed by its oxidation state written in Roman numerals and in parentheses. For example: Ni2 (OH) 4SO3 would be nickel (III) tetrahydroxytrioxosulfate (IV).
    • Mixed salts. They are produced by replacing the hydrogens of an acid with metal atoms of different hydroxides. Its nomenclature is identical to that of acid salts, but including both elements. For example: sodium potassium tetraoxosulfate (NaKSO4).

IUPAC nomenclature

The IUPAC (acronym for International Union of Pure and Applied Chemistry, that is, International Union of Pure and Applied Chemistry) is the organization International dedicated to establishing the universal rules of chemical nomenclature.

His system, proposed as a simple and unifying system, is known as the IUPAC nomenclature and differs from the traditional nomenclature in that it is more specific when naming compounds, since it not only names them but also clarifies the amount of each chemical element. in the compound.

!-- GDPR -->