Nomenclature of Alkenes, Alkynes & Functional Groups
Welcome to Lecture 14 of the CHEMCA Bridge Course! After mastering alkanes, we now step into unsaturated systems and functional groups. In this session, Abhishek Sengar Sir details parent chain selections with multiple bonds, alphabetical tie-breakers between double and triple bonds, and the IUPAC functional group seniority hierarchy.
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In-Depth Lecture Notes & Summary
Nomenclature of Alkenes & Alkynes
Unsaturated hydrocarbons contain carbon-carbon double bonds ($\text{C}=\text{C}$) or triple bonds ($\text{C}\equiv\text{C}$). Their naming follows specific adjustments to standard alkane rules:
1. Parent Chain Selection: The selected parent carbon chain must contain the maximum number of multiple bonds, even if it is not the longest continuous carbon chain in the molecule.
2. Numbering Priority: Number the parent chain from the end that gives the lowest possible locant to multiple bonds. Substituents (alkyl groups, halogens) are given lower priority during numbering compared to double/triple bonds.
Double vs. Triple Bond Tie-Breaker Rule
If a double bond and a triple bond are present at symmetrical positions from both ends of the parent chain, the double bond is given lower locant numbering priority due to alphabetical ordering ("ene" comes before "yne"):
$\text{HC}\equiv\text{C}-\text{CH}_2-\text{CH}=\text{CH}_2 \implies \text{Pent-1-en-4-yne}$ (Not Pent-4-en-1-yne)
Functional Group Seniority Hierarchy
When a compound contains more than one chemical functional group, one group is designated as the **Principal Functional Group** (written as the secondary suffix) based on IUPAC seniority. All other remaining functional groups are treated as **Substituents** (written as prefixes).
Seniority Group Explorer
Click any functional group in the dropdown list (arranged in exact descending seniority) to inspect its IUPAC prefix, suffix, and structural properties.
Group Properties: -COOH
Ethanoic acid
CH₃-COOH
Lecture 14 Concept Test
Validate your understanding of unsaturated numbering and priority ties.
Confused by Priority Ties?
If you are struggling with the alphabetical priority rules or choosing suffixes in polyfunctional compounds, email Abhishek Sir directly!
Email Support →Solved Unsaturated & Functional Naming Gallery
Select any of the 5 organic compounds discussed in class to display its chemical structure, formula, and complete IUPAC nomenclature proof.
Pent-2-ene
Condensed: CH₃-CH=CH-CH₂-CH₃
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