Fun. group formula → C ≡ C
Fun. Group name → carbon - carbon triple bond OR Acetylenic triple bond.
Definition : The aliphatic, unsaturated, hydrocarbons containing ( C ≡ C ) carbon carbon triple bond is called alkynes.
General Formula : CnH2n-2
Nomenclature : There are three system of nomenclature.
1. Common name system :
The common names of alkynes are derived from their sources. These common names are limited given below.
1) CH ≡ CH → Acetylene
2) CH3 - C ≡ CH → Allylene
3) CH3 - CH2- C ≡ CH → n,α-Crotonylene
4) CH3 - C ≡ C - CH3 → n,β-Crotonylene
2. Derived System
I) According to this system first member of CH ≡ CH called Acetylene.
II) The remaining member are considered the alkyl derivatives of Acetylenes & called alkyl acetylenes.
III) Use the prefix 'di' when two alkyl groups are similar & attached to acetylene part of group.
IV) When two alkyl groups different attached to Acetylene part given their names by alphabetical order.
V) Use the prefixes n, Iso, Neo, sec & tert for alkyl groups. Whenever necessary.
3. IUPAC system
Following rules are used to determine the IUPAC names of Acetylenes.
Rule No. 1:
Select the longest carbon chain containing C ≡ C group count the number of carbon atoms in normal chain only.
Find the name of parent alkane.
Replace ending 'ane' suffix with 'yne' suffix. Hence it becomes alkune.
Rule No. 2:
Start numbering from that terminal carbon atom nearest to C ≡ C group.
Rule No. 3:
Give the name & position of branched group.
Give the position of C ≡ C group.
Rule No. 4:
If alkyne contains 2,3,4 similar branched groups, use the prefixes di, tri & tetra respectively.
Rule No. 5:
If alkyne contains dissimilar branched groups. Give their names by alphabetical order.
| SL. No | Formula | Common name | IUPAC name | ||
| 1 |  |
Methylchloride | chloromethane | ||
| 2 |  |
Ethylbromide | bromoethane | ||
| 3 |  |
n-Propyliodide | 1-iodopropane | ||
| 4 |  |
n-Butylbromide | 1-bromobutane | ||
| 5 |  |
Isobutylchloride | 1-chloro-2-methylpropane | ||
| 6 |  |
Sec.butylbromide | 2-bromobutane | ||
| 7 |  |
tert.butylchloride | 2-chloro-2-methylpropane | ||
| 8 |  |
Neopentyliodide OR Neoamyliodide |
1-iodp-2,2-dimethylpropane |