Chemistry Bridge Course - Lecture 13 | CHEMCA JEE & NEET

CHEMCA

JEE & NEET Academy by Abhishek Sengar

Lecture 13 Organic Foundations Target: Class 10 to 11 Transition (JEE/NEET)

Introduction to IUPAC Nomenclature of Organic Compounds

Welcome to Lecture 13 of the CHEMCA Bridge Course! Nomenclature is the primary language of Organic Chemistry. In this session, Abhishek Sengar Sir introduces the structured 5-Part IUPAC Layout. Discover parent carbon chains, lowest locant rules, first point of difference, alphabetical writing hierarchies, and how to decode bond-line molecular formulas.

Video Lecture Broadcast

Instructor: Abhishek Sengar Sir Published: April 28, 2026 Subject: Organic Nomenclature

Interactive Lecture Timestamps

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In-Depth Lecture Notes & Summary

The 5-Part IUPAC Layout

Just like human names have prefix titles, first names, middle names, and surnames, an organic compound's systematic IUPAC name consists of 5 specific structural sections arranged sequentially:

[Sec. Prefix] + [Pri. Prefix] + [Root Word] + [Pri. Suffix] + [Sec. Suffix]

1. Root Word (Central core): Represents the number of carbon atoms in the parent carbon chain. E.g., $C_1 = \text{meth}$, $C_2 = \text{eth}$, $C_3 = \text{prop}$, $C_4 = \text{but}$, $C_5 = \text{pent}$, $C_6 = \text{hex}$.

2. Primary Suffix (Chain nature): Represents whether the carbon chain is saturated or unsaturated. E.g., $-ane$ (single), $-ene$ (double), $-yne$ (triple).

3. Secondary Suffix (Functional Group): Represents the primary functional group. E.g., $-ol$ (alcohol, $-OH$), $-al$ (aldehyde, $-CHO$), $-oic \text{ acid}$ (carboxylic, $-COOH$), $-one$ (ketone, $=O$).

4. Primary Prefix (Structure): Used if the carbon chain is cyclic. E.g., $cyclo-$, $bicyclo-$, $spiro-$. For open chains, it is omitted.

5. Secondary Prefix (Substituents): Represents branches, alkyl groups, and any secondary functional groups. E.g., $-CH_3 = \text{methyl}$, $-C_2H_5 = \text{ethyl}$, $-Cl = \text{chloro}$.

5 Important Rules of IUPAC Notation

To write a structurally flawless IUPAC name, Abhishek Sengar Sir details 5 crucial orthographic rules:

1. Casing: Only the very first letter of the systematic name is capitalized; all other letters must be lowercase (e.g., 2-Methylpentane).

2. No Spaces: The systematic name is written as one single continuous word without any spaces between letters.

3. Hyphens (-): Numbers and alphabets are always separated by a hyphen (e.g., 2-methyl, 4-ethyl).

4. Commas (,): Multiple consecutive numbers are separated by commas (e.g., 2,2-dimethyl, 2,3,5-trimethyl).

5. Dropping 'e': Drop the trailing "e" of the primary suffix ($-ane, -ene, -yne$) if the subsequent secondary suffix starts with a vowel ($a, e, i, o, u$) or $y$.
$$\text{methane} + \text{ol} \to \text{methan-ol} \to \text{methanol}$$

IUPAC Rules for Alkanes

When naming branched alkanes, the systematic procedure involves:

Step 1: Selection of Parent Carbon Chain Identify and select the longest continuous carbon chain as the parent chain. Any carbons outside this chain are treated as substituents (branches).

Step 2: Numbering (Lowest Locant / First Point of Difference) Number the parent chain from the end that gives the lowest possible locants to the substituents. If multiple numbering paths give different locant sets, compare them term-by-term. The set that has the lower number at the first point of difference is selected.
Example: (2,3,5) is preferred over (2,4,5) because 3 is smaller than 4.

Step 3: Alphabetical Priority Write the substituents in alphabetical order. Prefixes like $di-, tri-, tetra-$ are ignored when deciding alphabetical priority (e.g., $ethyl$ comes before $dimethyl$).
If identical locant sets are obtained from both ends, assign the lower locant to the substituent that comes first alphabetically (e.g., 3-ethyl-4-methylhexane is preferred).

5-Part IUPAC Builder

Select components to build a custom IUPAC name. Watch the spelling engine apply drop-e and hyphens rules dynamically!

Secondary Prefix (Substituents)

Primary Prefix (Structure)

Root Word (Chain Length)

Primary Suffix (Bonds)

Secondary Suffix (Group)

Assembled IUPAC Name 2-Methylpentan-1-ol

E was dropped before 'ol'.

Homework Solver

View the detailed, step-by-step nomenclature proofs for the two bond-line structures assigned by Abhishek Sir at the end of class.

Homework Structure 1

IUPAC Name: 2,4-Dimethylpentane

• Parent chain: Longest continuous carbon chain has 5 carbons (pentane).
• Numbering: Equal distance from both ends (branches at 2 and 4). Locant set is (2,4) either way.
• Name: 2,4-Dimethylpentane.

Homework Structure 2

IUPAC Name: 3-Ethyl-2,4-dimethylpentane

• Parent chain: The longest chain is a 5-carbon pentane chain.
• Numbering: Identical locant set (2,3,4) from both sides.
• Name: Eth- comes alphabetically before meth-, written as: 3-Ethyl-2,4-dimethylpentane.

Lecture 13 Concept Test

Validate your understanding of nomenclature rules and prefix priorities instantly.

Question 1 of 5

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Confused by Locants?

If you have doubts regarding parent chain selections, the "First Point of Difference" rule, or naming cyclic systems, email Abhishek Sengar Sir directly!

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Solved Alkanes & Branches Gallery

Select any of the 6 major compounds discussed in class to display its interactive chemical structure, formula, and complete nomenclature proof.

Alcohol

Methanol

Condensed: CH₃OH

Explanation goes here...

Root: meth Pri. Suffix: an Sec. Suffix: ol Prefix: None

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Chemistry Bridge Course Lecture 13