Chapter Summary
This chapter introduces the systematic naming of organic compounds and the fascinating world of isomerism. The chapter covers three main areas:
Nomenclature of Organic Compounds: Learn the IUPAC rules for naming different types of organic compounds including alkanes with branches, unsaturated hydrocarbons, and compounds with functional groups like alcohols, carboxylic acids, aldehydes, ketones, halo compounds, and ethers.
Functional Groups: Understand how specific atoms or groups of atoms attached to carbon chains determine the chemical and physical properties of organic compounds. Common functional groups include hydroxyl (-OH), carboxyl (-COOH), aldehyde (-CHO), keto (C=O), halo groups, and alkoxy groups.
Isomerism: Explore how compounds with the same molecular formula can have different structures and properties. The chapter covers chain isomerism, position isomerism, functional isomerism, and metamerism.
Question and Answer Section
Basic Nomenclature Questions
Q1: What is the IUPAC name for the compound CH₃-CH₂-CH₂-CH₂-CH₃?
Answer: The compound has 5 carbon atoms in a straight chain. The word root for 5 carbons is "pent" and since it's an alkane, the suffix is "ane". Therefore, the IUPAC name is pentane.
Q2: How do you name a branched alkane with one branch?
Answer: Follow these IUPAC rules:
- Select the longest carbon chain as the main chain
- Number the chain so the branch gets the lowest position number
- Name the branch as an alkyl group (methyl, ethyl, propyl, etc.)
- Write the name as: position number + hyphen + alkyl group name + main chain name
- Example: 2-methylpentane
Q3: What is the IUPAC name for CH₃-CH(CH₃)-CH₂-CH₃?
Answer:
- Main chain has 4 carbons (butane)
- Branch is a methyl group at position 2
- IUPAC name: 2-methylbutane
Functional Groups Questions
Q4: What is a functional group? Give three examples.
Answer: A functional group is an atom or group of atoms bonded to carbon in an organic compound that determines the distinctive chemical and physical properties of that compound.
Examples:
- Hydroxyl group (-OH) found in alcohols
- Carboxyl group (-COOH) found in carboxylic acids
- Aldehyde group (-CHO) found in aldehydes
Q5: How do you name alcohols according to IUPAC rules?
Answer: To name alcohols:
- Replace 'e' in the corresponding alkane name with 'ol'
- For alcohols with more than 2 carbons, specify the position of the -OH group
- Number the chain so the -OH group gets the lowest position number
- Format: alkane name - e + hyphen + position number + hyphen + ol
- Example: CH₃-CH₂-CH₂-OH is propan-1-ol
Q6: What is the IUPAC name for CH₃-COOH?
Answer: This compound has a carboxyl group (-COOH). Count the total carbon atoms including the one in the carboxyl group (2 carbons). Replace 'e' in ethane with 'oic acid'. The IUPAC name is ethanoic acid.
Unsaturated Hydrocarbons Questions
Q7: How do you name alkenes according to IUPAC rules?
Answer: For alkenes:
- Number the carbon chain so the double bond gets the lowest position number
- Use the format: word root + hyphen + position of double bond + hyphen + ene
- Example: CH₂=CH-CH₂-CH₃ is but-1-ene
Q8: What is the difference between but-1-ene and but-2-ene?
Answer: Both have the same molecular formula (C₄H₈) but different positions of the double bond:
- But-1-ene: CH₂=CH-CH₂-CH₃ (double bond between carbons 1 and 2)
- But-2-ene: CH₃-CH=CH-CH₃ (double bond between carbons 2 and 3)
Isomerism Questions
Q9: What are isomers? Define isomerism.
Answer: Isomers are compounds having the same molecular formula but different chemical and physical properties due to different structural arrangements. Isomerism is the phenomenon where compounds with identical molecular formulas exhibit different structures and properties.
Q10: Explain chain isomerism with an example.
Answer: Chain isomerism occurs when compounds have the same molecular formula but different carbon chain structures.
Example: C₄H₁₀ has two chain isomers:
- CH₃-CH₂-CH₂-CH₃ (straight chain - butane)
- CH₃-CH(CH₃)-CH₃ (branched chain - 2-methylpropane)
Q11: What is position isomerism? Give an example.
Answer: Position isomerism occurs when compounds have the same molecular formula and functional group but differ in the position of the functional group.
Example: C₃H₈O with -OH group:
- CH₃-CH₂-CH₂-OH (propan-1-ol)
- CH₃-CH(OH)-CH₃ (propan-2-ol)
Q12: Distinguish between functional isomerism and metamerism.
Answer: Functional Isomerism: Compounds with same molecular formula but different functional groups. Example: C₂H₆O can be CH₃-CH₂-OH (alcohol) or CH₃-O-CH₃ (ether)
Metamerism: Compounds with same molecular formula but different alkyl groups on either side of a bivalent functional group. Example: C₄H₁₀O ethers - CH₃-CH₂-O-CH₂-CH₃ and CH₃-O-CH₂-CH₂-CH₃
Advanced Application Questions
Q13: Write the structural formula for 2,3-dimethylpentane and name its isomers.
Answer: Structural formula: CH₃-CH(CH₃)-CH(CH₃)-CH₂-CH₃
This compound exhibits chain isomerism with other C₇H₁₆ compounds like:
- Heptane (straight chain)
- 2-methylhexane
- 3-methylhexane
- 2,2-dimethylpentane
Q14: How many position isomers are possible for pentanol (C₅H₁₂O)?
Answer: Pentanol can have 3 position isomers based on the position of the -OH group:
- Pentan-1-ol: CH₃-CH₂-CH₂-CH₂-CH₂-OH
- Pentan-2-ol: CH₃-CH₂-CH₂-CH(OH)-CH₃
- Pentan-3-ol: CH₃-CH₂-CH(OH)-CH₂-CH₃
Q15: Identify the type of isomerism between CH₃-CH₂-CHO and CH₃-CO-CH₃.
Answer: These compounds show functional isomerism because they have:
- Same molecular formula (C₃H₆O)
- Different functional groups (aldehyde -CHO vs ketone C=O)
- Different names (propanal vs propanone)
Practice Questions
Q16: Write IUPAC names for the following compounds: a) CH₃-CH₂-CH(Cl)-CH₃ b) CH₃-CH=CH-CH₂-CH₃
c) CH₃-CH₂-O-CH₃
Answer: a) 2-chlorobutane (halo compound) b) pent-2-ene (alkene) c) methoxyethane (ether)
Q17: What type of isomerism is exhibited by the following pairs? a) CH₃-CH₂-CH₂-CH₃ and CH₃-CH(CH₃)-CH₃ b) CH₃-CH₂-OH and CH₃-O-CH₃
Answer: a) Chain isomerism (different carbon chain arrangements) b) Functional isomerism (alcohol vs ether functional groups)
Key Points to Remember
- Always identify the longest carbon chain as the main chain when naming compounds
- Number the chain to give functional groups and branches the lowest possible position numbers
- Functional groups determine the properties and naming of organic compounds
- Isomers have the same molecular formula but different structures and properties
- Different types of isomerism include chain, position, functional, and metamerism
- Practice drawing structural formulas to better understand isomerism concepts
This study material provides a comprehensive understanding of organic nomenclature and isomerism concepts essential for Class 10 students following the Kerala syllabus.