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Organic Chemistry – Some Basic Principles and Techniques - IUPAC Nomenclature of Organic Compounds

Grade 11CBSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The IUPAC name of an organic compound consists of three main parts: WordRootWord Root, SuffixSuffix, and PrefixPrefix. The general format is: SecondaryPrefix+PrimaryPrefix+WordRoot+PrimarySuffix+SecondarySuffixSecondary Prefix + Primary Prefix + Word Root + Primary Suffix + Secondary Suffix.

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The WordRootWord Root denotes the number of carbon atoms in the longest continuous chain (e.g., C1C_1: Meth-, C2C_2: Eth-, C3C_3: Prop-, C4C_4: But-).

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The PrimarySuffixPrimary Suffix indicates the saturation or unsaturation in the carbon chain: −ane-ane for alkanes, −ene-ene for alkenes, and −yne-yne for alkynes.

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The SecondarySuffixSecondary Suffix is used to represent the principal functional group (e.g., −ol-ol for alcohols, −al-al for aldehydes, −one-one for ketones, and −oic acid-oic\ acid for carboxylic acids).

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The PrefixPrefix is used to indicate the presence of side chains or substituent groups (e.g., −CH3-CH_3 is methyl, −C2H5-C_2H_5 is ethyl, −Cl-Cl is chloro).

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Longest Chain Rule: Select the longest continuous chain of carbon atoms as the parent chain. If a functional group is present, it must be part of this chain.

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Lowest Locant Rule: Number the carbon atoms of the parent chain such that the substituents or functional groups get the lowest possible locant (number).

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Priority Order of Functional Groups: −COOH>−SO3H>−COOR>−COCl>−CONH2>−CN>−CHO>>C=O>−OH>−NH2>C=C>C≡C>-COOH > -SO_3H > -COOR > -COCl > -CONH_2 > -CN > -CHO > >C=O > -OH > -NH_2 > C=C > C \equiv C > Substituents (Halogens, Nitro, Alkyl).

📐Formulae

CnH2n+2 (General formula for Alkanes)C_n H_{2n+2} \text{ (General formula for Alkanes)}

CnH2n (General formula for Alkenes)C_n H_{2n} \text{ (General formula for Alkenes)}

CnH2n−2 (General formula for Alkynes)C_n H_{2n-2} \text{ (General formula for Alkynes)}

IUPAC Name=Prefix+Word Root+Primary Suffix+Secondary Suffix\text{IUPAC Name} = \text{Prefix} + \text{Word Root} + \text{Primary Suffix} + \text{Secondary Suffix}

💡Examples

Problem 1:

Give the IUPAC name for CH3−CH(Cl)−CH(CH3)−CH2−OHCH_3-CH(Cl)-CH(CH_3)-CH_2-OH.

Solution:

3-chloro-2-methylbutan-1-ol

Explanation:

  1. The longest chain containing the −OH-OH group has 4 carbons (Butane). 2. Numbering starts from the carbon attached to −OH-OH (priority). 3. Chlorine is at C3C_3 and Methyl is at C2C_2. 4. Alphabetically, Chloro comes before Methyl.

Problem 2:

Name the compound: CH3−CO−CH2−CH2−COOHCH_3-CO-CH_2-CH_2-COOH.

Solution:

4-oxopentanoic acid

Explanation:

  1. The chain has 5 carbons. 2. The principal functional group is the carboxylic acid (−COOH-COOH), which gets the suffix '-oic acid' and position 1. 3. The ketone group (>C=O>C=O) is treated as a substituent called 'oxo' at position 4.

Problem 3:

Write the IUPAC name for CH2=CH−CH(CH3)2CH_2=CH-CH(CH_3)_2.

Solution:

3-methylbut-1-ene

Explanation:

  1. The longest chain with the double bond has 4 carbons (Butene). 2. Numbering starts from the double bond end. 3. A methyl group is present at the 3rd carbon.
IUPAC Nomenclature of Organic Compounds Revision - Class 11 Chemistry CBSE