Alkane Alkene Alkyne Nomenclature: Overview, IUPAC, FAQs

In accordance with the IUPAC Nomenclature, which is a systematic system for naming organic chemical compounds, a single compound may have a number of valid systematic names. However, no two compounds may share the same name. The most basic hydrocarbons that we are aware of are alkanes. CnH2n+2 is the general formula for alkanes. Only sigma bonds connect the carbon and hydrogen atoms in alkanes. They come together to form a series that shares the same functional group and is distinguished from other members by a "CH2" group, known as the homologous series. They are unsaturated hydrocarbons called alkenes and alkynes. Triple-bond couplings are found in alkynes, while double-bond linkages are found in alkenes.

Overview

The simplest hydrocarbons that we are aware of are alkanes. They often have the formula CnH2n+2. Alkanes are a subclass of saturated hydrocarbons, meaning that the only bonds separating the atoms of carbon and hydrogen in them are sigma bonds. The successive compounds in the homologous series of organic compounds share the same functional group and are distinct from one another by a "-CH2" group.

As opposed to this, unsaturated hydrocarbons like alkenes and alkynes are. Alkenes exhibit double-bond couplings, whereas alkynes exhibit triple-bond links. The following paragraphs address the rules for IUPAC nomenclature of alkanes, alkenes, and alkynes:

In the case of alkanes, the longest hydrocarbon chain is chosen and is referred to as the parent chain. The parent chain for alkenes and alkynes is a hydrocarbon chain with a double or triple bond. Greek alphabets like octa and hepta are used to name the parent chain.

Alkanes have the suffix "-ane," alkenes have the suffix "-ene," and alkynes have the suffix "-yne." For instance, C2H6 is referred to as ethane, C2H4 is referred to as ethene, and C2H2 is referred to as ethyne.

In order to get to the double- or triple-bonded carbon atom first, the parent chain is numbered. Numbers are used to indicating where the carbon atom is in relation to the double bond. Pent-2-ene is the term given to CH3CH=CHCH2CH3, for instance.

Greek numerical prefixes like di and tri are used to indicate the number of double bonds when there are several of them throughout the carbon chain.

IUPAC Nomenclature

Most compounds with the same structural formula were formerly referred to by various names based on the areas in which they were produced. This naming scheme was extremely insignificant because it caused so much confusion. Finally, IUPAC (International Union for Pure and Applied Chemistry) established a uniform name system incorporating the guidelines for naming substances. IUPAC nomenclature or name is the term used to describe this naming convention.

Nomenclature One key distinction between the language of chemistry and other sciences and natural languages is how things are named. The other is that written language is more significant than spoken language. Not only must elements and compounds be named in chemistry, but also the methods used in reactions, the equipment used, and theoretical concepts.

Nomenclature Of Alkanes

All alkanes have names that end in -ane. Every carbon-hydrogen chain that lacks any double bonds or functional groups is referred to by the suffix -ane, regardless of whether the carbons are bonded end-to-end in a ring (in which case they are known as cyclic alkanes or cycloalkanes) or if they have side chains and branches.

The number of carbons in the chain serves as the sole identifier for alkanes with unbranched carbon chains. According to the number of carbon atoms in each, the series' first four members are known as:

  • CH4 = methane

    • Methane is one carbon atom that has been saturated with hydrogen and has the chemical formula CH4.

  • C2H6 = ethane

    • Ethane is made up of two hydrogen-saturated carbons, or C2H6.

  • C3H8 = propane

    • With the help of the chemical formula C3H8, propane is expressed.

  • C4H10 = butane

    • Four hydrogen-saturated carbons make up butane, which is represented by the formula C4H10.

The suffix -ane is added to the relevant numerical multiplier to name alkanes having five or more carbon atoms, with the exception that the fundamental numerical term's terminal -a is dropped. Thus, C5H12 is referred to as pentane, C6H14 as hexane, C7H16 as heptane, and so on.

  • IUPAC Rules for Alkanes Nomenclature

  1. Decide which carbon chain is the longest. The parent chain is this group of links.

  2. List every possible replacement (groups appending from the parent chain).

  3. Starting at the end of the chain closest to a substituent group, sequentially number the chain.

  4. Indicate each substituent group's location with the relevant number and name.

  5. Put the name together by listing the groups alphabetically using the whole name (e.g. cyclopropyl before isobutyl). When alphabetizing, the prefixes di, tri, tetra, etc., which are used to identify several groups of the same kind, are ignored.

Nomenclature of Alkenes

The many structural kinds that a hydrocarbon might represent are revealed by its molecular formula. Take molecules with the formula C5H8 as an example. Pentane, an alkane with five carbons, has a formula of C5H12, hence the difference in hydrogen concentration is 4. Due to this distinction, it is possible for such compounds to have two rings, a triple bond, two double bonds, a ring, or three rings. There are at least fourteen more examples in addition to the ones that are given here.

Therefore, much like with alkanes, a uniform naming system must be used to distinguish between the different types of these unsaturated compounds. The most basic are the cycloalkane-like alkenes, which are unsaturated hydrocarbons with functional groups attached to carbon-carbon double bonds and have the same chemical formula as cycloalkanes.

IUPAC Rules for Alkene Nomenclature

  1. An alkene or cycloalkene is indicated by the one suffix (ending).

  2. Both carbon atoms in the double bond must be present in the root name's longest chain.

  3. Beginning with the end closest to a carbon atom in a double bond, the root chain must be numbered. The nearest substituent rule is used to identify the end where numbering begins if the double bond is in the middle of the chain.

  4. The double bond locator is the smallest of the two integers identifying the carbon atoms in the double bond.

  5. The compound is given a name with a diene, triene, or comparable prefix to indicate the number of double bonds present, and each double bond is given a locator number.

The following are substitute groups with double bonds:

  • H2C=CH– Vinyl group

  • H2C=CH–CH2– Allyl group

Nomenclature of Alkynes

The empirical formula for alkynes is CnH2n2, and they are organic compounds comprised of functional group carbon-carbon triple bonds. They are hydrocarbons with unsaturation. When there is only one alkyne in the molecule, alkynes use the suffix -yne, similar to how alkenes use the ending -ene. The carbon chain is numbered so that the initial multiple bonds gets a lower number if a molecule has both a double and a triple bond. The double bond takes precedence when both bonds may be given the same number. The name "n-en-n-yne" is then given to the molecule, with the double bond root name coming before the triple bond root name (e.g. 2-hepten-4-yne).

  • IUPAC Rules for Alkynes Nomenclature

  1. Determine the longest carbon chain that contains the triple bond's two carbons.

  2. Begin numbering the longest chain at the end that is most near the triple bond. Alkynes in any other position are referred to as internal alkynes, while a 1-alkyne is referred to as a terminal alkyne.

  3. Label each of the substituents at the corresponding carbon after numbering the longest chain with the lowest number given to the alkyne. Put the substituents in alphabetical order and then write the name of the molecule. Use the prefixes di, tri, and tetra for two, three, and four substituents, respectively, if there are multiples of the same substituent. The alphabetical order of these prefixes is not taken into consideration.

  4. If the molecule contains alcohol, number the longest chain starting at the end that is closest to it and adheres to the same guidelines. However, since the alcohol group takes precedence over the triple bond, the suffix would be -ynol.

  5. Find the longest carbon chain that includes both the triple bonds when the molecule contains two triple bonds. Starting at the end that is closest to the triple bond that appears initially, count the longest chain. This molecule's name would be completed with the suffix -diyne.

  6. Alkynyl substitutes are those that have a triple bond in them.

  7. An alkyne is a molecule that has both double and triple bonds. Starting with the end nearest to the functional group that occurs first, the chain can be numbered.