Nomenclature of Alkynes

Alkynes are the unsaturated hydrocarbons having at least one C- C bond. IUPAC nomenclature is used for giving names to organic compounds. In the early days, most of the compounds with the same structural formula have been recognized by different names relying on the regions in which they had been synthesized. But, this method was complex for naming compounds. Hence, IUPAC Nomenclature was considered a common naming system and it is a very easy and not complex method for naming them. IUPAC stands for INTERNATIONAL UNION for PURE and APPLIED CHEMISTRY.

Alkynes

As we studied above, Alkynes are organic compounds which have a carbon-carbon triple bond, and their empirical formula Is C_nH_2n-2.

Here, a list of the first ten carbon chain alkynes is given with their name and their molecular formula.

Industrially most commonly used alkyne is Ethyne which has the common name Acetylene. 

Basic rules for naming in IUPAC Nomenclature

A set of logical rules found and used by organic chemists to give a name to any organic compound is known as the IUPAC nomenclature system. 

If you know the rules of IUPAC, then you can find the common name of any of the structural formulas and for any IUPAC name, you can find the structural formula.

Three salient features of IUPAC nomenclature are given below:-

1. There must be a root or base chain or ring of carbon atoms in the molecular structure.

2. Functional groups present in the compound are named by Suffix or other elements. According to the priority of functional groups, some functional group’s naming comes in prefixes and one post preferred group comes into a suffix.

3. Presence of substituent groups like hydrogen, these substituent groups complete the molecular structure.

IUPAC NAMING OF ALKYNES

Following rules are used for finding IUPAC names of the alkynes.

1. Select the longest hydrocarbon chain, which is termed as parent/ root or base chain. In the case of alkynes, the chain which is having triple bond will be considered a Root or parent, or base chain. The name of the parent chain is termed with the help of IUPAC. 

2. Start numbering the carbons in the longest carbon chain, in alkynes numbering will start from that end to which the triple bond is closest.

3. 1-alkyne will be referred to as terminal alkynes and other triple bonds present in the compound will be referred to as terminal alkynes.

4. After numbering, the next step is naming the compound, remembering that naming should be done according to alphabetical order.               

5. For more than one same substituent group present in the same compound we have to use prefixes like di, tri, tetra, etc. For two, three, and four respectively.

6. Substituent groups that have triple bonds are known as alkynyl.

7. Compounds that contain both alkene and alkyne groups are known as alkyne. Numbering will start with a functional group that is closest to the terminal.

8. If both alkene and alkyne are at the same distance then, preference will be given to alkene.

Examples

Write the IUPAC name of the following structures of compounds.

1.

                                            IUPAC Name : 4-methyl-1,5-octadiyne         

2.    IUPAC Name : 2-methyl-1-pentene-3-yne     

3.                                                                                                                                           IUPAC Name : 3-butyn-2-ol

4.                                                   

IUPAC Name :  2,2,9-triiodo-5-methyl-non-3-yne                         

5.        IUPAC Name : 4-methyl-1,5-octadiyne     

Draw the structure by using following IUPAC names

1. Pent-2-yne                                                                                                   

2.  Hexa-1,3-dien-5-yne          

3. 5-ethynyl-1,3,6-heptatriene

4. 4-vinyl-1-hepten-5-yne

5. Cyclooctyne

Hence, these are some examples of IUPAC naming. You will face these two types of questions, first, you are given names and you have to write IUPAC naming and the second one is you have IUPAC names and you have to draw their structures. Both examples are discussed above.

That’s all about the IUPAC nomenclature of Alkynes.

Conclusion

Alkynes are those hydrocarbons which have one or more triple bonds in them. General empirical formula of alkynes is CnH2n-2. We read about IUPAC nomenclature and its basic rule, naming of IUPAC compounds. We have tried explaining the nomenclature of alkynes with the structure and also explained how to name the structure by looking at the structure.