Introduction IUPAC Nomenclature
The proliferation of organic chemistry gave rise to a number of organic compounds with broadly the same structural formula. To ensure that the nomenclature of such compounds was homogenized and was not at odds with one another, a set of rules were established by the International Union for Pure and Applied Chemistry. Thus, the nomenclature of alkanes, for instance, would differ based upon the IUPAC system. Let us look at the IUPAC names of alkane, alkene, and alkyne along with the rules for naming such compounds.
What is IUPAC Nomenclature?
A single chemical compound can have multiple acceptable systematic names and the systematic method that is employed for the naming of organic chemical compounds is called IUPAC Nomenclature but no two compounds can have the same name.
IUPAC Nomenclature
Earlier, the compounds with the same structural formula were called by different names depending on the regions where they were synthesized or produced. This naming system was very trivial as it raised a lot of confusion. Then a common naming system enlisting the standard rules was set up by IUPAC (International Union for Pure and Applied Chemistry) for naming compounds. This method of naming is known as IUPAC nomenclature.
In chemistry there are several nomenclatures: apart from elements and compounds, reactions methods, pieces of apparatus, and theoretical concepts are also named leading to a very organized and systematic process.
IUPAC Nomenclature of Alkanes, Alkynes, and Alkenes
This method of naming is known as the IUPAC nomenclature. IUPAC nomenclature of alkanes, alkynes, and alkenes are described below:
Alkanes are the simplest hydrocarbons that we know. The general formula for Alkanes is \[CnH_{2n + 2}\]. Alkanes only have sigma bond linkages between carbon and hydrogen. They form a series, known as the homologous series, which contain the same functional group and differ from one another by a ‘\[CH_{2}\]’ group.
Alkenes and alkynes are unsaturated hydrocarbons. Alkenes contain double bond linkages and in alkynes, triple bond linkages are present.
Rules for the IUPAC Nomenclature of Alkanes, Alkenes, and Alkynes are Given Below:
Firstly the longest hydrocarbon chain is selected, which is known as the parent chain in alkanes. Therefore in the case of alkenes and alkynes, the hydrocarbon chain with the double and triple bond is chosen as the parent chain. While naming the parent chain Greek alphabets such as hepta, octa, etc are used.
For alkanes the suffix ‘-ane’ is used, for alkenes, the suffix ‘-ene’ is used. Similarly the suffix ‘yne’ is used for alkynes. For example, \[C_{2}H_{6}\] is called ethane, \[C_{2}H_{4}\] is called ethene and \[C_{2}H_{2}\] is called ethyne.
The parent chain is numbered in such a manner that we reach the double-bonded or triple bonded carbon atom first. The position of the carbon atom having a double bond is mentioned in numerals. For example, \[CH_{3}CH = CHCH_{2}CH_{3}\] is named Pent-2-ene.
If there are multiple double bonds in the carbon chain, prefixes such as di, tri are used to denote their number.
FAQs on Nomenclature of Alkane, Alkene and Alkyne
1. How do you Identify an Alkene or an Alkyne?
While it is very easy to identify an alkane due to its relatively simple structure, the confusion usually is between identifying alkenes and alkynes. The fundamental difference between alkanes and alkenes are the presence of double bonds and triple bonds between carbon-carbon atoms, respectively. Alkene compounds end with the suffix -ene, and alkyne compounds end with the suffix -yne.
When it comes to chemical tests, bromine water can also be used to differentiate between alkanes and alkenes. Since alkene contains double bonds between carbon-carbon atoms, the bromine water which is brown in colour turns colourless. This result can be observed on any unsaturated compounds with double bonds in them.
2. What are Some of the Rules you Must Follow while Writing the Names of the Compounds?
IUPAC observes certain naming conventions involving the nomenclature of alkenes, alkanes and alkynes. The basename of the compound is derived from the number of carbons present in the longest carbon chain. Among special characters, only dashes and commas are used. Commas are used while writing numbers and dashes are used for both letters and numbers. The name, however, should be written without any spaces.
3. Where can I find useful study resources for the nomenclature of alkane, alkene and alkyne?
You can find everything you need on the Vedantu app or website. These resources are created by professionals and the content is accurate and reliable. Students can find information related to nomenclature, hydrocarbons and a whole lot more! These study materials are completely free and there is no cost involved. All students just have to sign in and then you will be able to download what you want in pdf format. Students can take advantage of these free resources that will surely help them ace their exams.
4. How do you identify an alkene?
Alkenes are unsaturated molecules. Alkenes consist of at least one double bond of carbon-carbon which displaces two atoms of hydrogen. It means alkenes do not have the maximum number of hydrogen atoms. In order to determine the difference between alkane and alkene, a simple bromine water test can be used. During this test alkene will turn brown bromine water colourless as the bromine reacts with the carbon-carbon double bond. This reaction can be used for determining unsaturated compounds containing double bonds in carbon-carbon form like alkene.
5. What is meant by IUPAC nomenclature?
Earlier, the compounds with the same structural formula were called by different names depending on the regions where they were synthesized or produced. This naming system was very trivial as it raised a lot of confusion. Then a common naming system enlisting the standard rules was set up by IUPAC (International Union for Pure and Applied Chemistry) for naming compounds. This method of naming is known as IUPAC nomenclature. In chemistry there are several nomenclatures: apart from elements and compounds, reactions methods, pieces of apparatus and theoretical concepts are also named leading to a very organized and systematic process.
6. What are the basic rules to be followed while naming the carbon compound?
Firstly the longest hydrocarbon chain is selected, which is known as the parent chain in alkanes. So for the case of alkenes and alkynes, the hydrocarbon chain with the double and triple bond is chosen as the parent chain. While naming the parent chain Greek alphabets such as hepta, octa, etc are used.
For alkanes the suffix ‘-ane’ is used, for alkenes, the suffix ‘-ene’ is used. Similarly the suffix ‘yne’ is used for alkynes. For example, \[C_{2}H_{6}\] is called ethane, \[C_{2}H_{4}\] is called ethene and \[C_{2}H_{2}\] is called ethyne. The parent chain is numbered in such a manner that we reach the double-bonded or triple bonded carbon atom first. The position of the carbon atom having a double bond is mentioned in numerals. For example, \[CH_{3}CH = CHCH_{2}CH_{3}\] is named as Pent-2-ene. If there are multiple double bonds in the carbon chain, prefixes such as di, tri is used to denote their number.
7. How do we name alkenes?
The longest carbon chain is selected as the parent alkene. The suffix ‘ene’ is used. If a double bond occurs twice or thrice the alkene is called diene or triene respectively. The position of double bonds is given by numbers 1, 2, 3 etc. The longest chain is numbered from the end, having the lowest number to the carbon atom of the double bond and written before the suffix ‘ene’. If while numbering the chain the double bond gets the same number from any side the carbon chain is numbered in such a way that the substituent gets the lowest number. If there are two or more double bonds, the lowest sum rule is followed. The name and position of other groups are indicated by prefixes.
