Organic Chemistry: Some Basic Principles and Techniques - NCERT Solutions

Chapter Overview

This chapter introduces the fundamental concepts of organic chemistry, providing the essential foundation for understanding complex organic reactions and mechanisms in JEE and NEET examinations.

Key Concepts:

• Tetravalency of carbon and catenation
• Structural representations of organic compounds
• Classification of hydrocarbons and functional groups
• Isomerism and stereochemistry basics
• Organic reaction mechanisms

NCERT In-Text Examples with Solutions

Example 10.1

Question: Identify the number of � and � bonds in the molecule: CH�=CH-CH=CH�

Solution:

Step 1: Draw the structure
H�C=CH-CH=CH�

Step 2: Count � bonds
- Each C-H bond is a � bond: 8 C-H bonds = 8 � bonds
- Each C-C single bond is a � bond: 1 C-C single bond = 1 � bond
- Each double bond contains 1 � bond: 2 double bonds = 2 � bonds
Total � bonds = 8 + 1 + 2 = 11 � bonds

Step 3: Count � bonds
- Each double bond contains 1 � bond: 2 double bonds = 2 � bonds

Answer: � bonds = 11, � bonds = 2

Example 10.2

Question: Write the IUPAC name of the following compound:

   CH�CH�CH�CH�
    |
   CH�

Solution:

Step 1: Identify the longest carbon chain
Longest chain has 4 carbon atoms = butane

Step 2: Identify substituents
One methyl group at position 2

Step 3: Apply IUPAC rules
Number from the end that gives the substituent the lowest number

Answer: 2-Methylbutane

Example 10.3

Question: Identify the functional group in the following compound:

CH�-CH�-CH�-OH

Solution:

Step 1: Analyze the structure
- Carbon chain: 3 carbons (propane)
- Functional group: -OH group

Step 2: Identify the functional group
-OH group is the alcohol functional group

Step 3: Name the compound
- Carbon chain + -OH = alcohol
- 3 carbons = prop + -ol = propanol
- OH group on first carbon (if numbered from OH side)

Answer: Propanol (alcohol functional group)

NCERT Exercise Solutions

Exercise 10.1

Question 1: What are hybridised carbon atoms? What are their types?

Solution: Hybridised carbon atoms are carbon atoms where orbitals of similar energy combine to form new hybrid orbitals.

Types of hybridisation:

1. sp hybridisation: 1 s + 1 p = 2 sp orbitals (linear, 180�)
2. sp� hybridisation: 1 s + 2 p = 3 sp� orbitals (trigonal planar, 120�)
3. sp� hybridisation: 1 s + 3 p = 4 sp� orbitals (tetrahedral, 109.5�)

Exercise 10.2

Question 2: Draw the structures of the following compounds: (a) 3-methylhex-1-ene (b) 4-ethylhex-2-yne

Solution:

(a) 3-methylhex-1-ene
   CH�=CH-CH(CH�)-CH�-CH�-CH�
   |   1   2   3    4   5   6
   - Methyl group at carbon 3
   - Double bond between C1 and C2

(b) 4-ethylhex-2-yne
   CH�-CaC-CH�-CH(CH�)-CH�
       1   2   3    4   5   6
   - Ethyl group at carbon 4
   - Triple bond between C2 and C3

Exercise 10.3

Question 3: Give the IUPAC name of the following compounds: (a) CH�-CH�-CH�-CH�-CH� (b) CH�-CH=CH-CH�

Solution:

(a) CH�-CH�-CH�-CH�-CH�
   - 5 carbon atoms in main chain
   - No substituents, no double/triple bonds
   - IUPAC name: Pentane

(b) CH�-CH=CH-CH�
   - 4 carbon atoms in main chain
   - Double bond between C2 and C3
   - Numbering: CH�-CH=CH-CH�
              1   2   3   4
   - IUPAC name: But-2-ene

Exercise 10.4

Question 4: Which of the following compounds are isomers of each other? (i) CH�-CH�-CH�-CH� (butane) (ii) CH�-CH(CH�)-CH� (isobutane) (iii) CH�-CH=CH-CH� (but-2-ene) (iv) CH�-CH�-CH�-OH (propanol)

Solution:

Isomers are compounds with the same molecular formula but different structures.

Molecular formulas:
(i) CH�-CH�-CH�-CH� = C�H��
(ii) CH�-CH(CH�)-CH� = C�H��
(iii) CH�-CH=CH-CH� = C�H�
(iv) CH�-CH�-CH�-OH = C�H�O

Analysis:
- (i) and (ii) both have C�H�� � They are isomers (chain isomers)
- (iii) has C�H� � Not an isomer of (i) or (ii)
- (iv) has C�H�O � Not an isomer of others

Answer: (i) and (ii) are isomers of each other

Exercise 10.5

Question 5: Explain the term ‘functional group’ with example.

Solution: A functional group is an atom or group of atoms that defines the characteristic chemical reactions of a family of organic compounds.

Example: Alcohol functional group (-OH)

• Compounds containing -OH group are called alcohols
• They show similar chemical properties
• Examples: CH�OH (methanol), CH�CH�OH (ethanol), (CH�)�COH (tert-butanol)

Other important functional groups:

• Carboxyl group (-COOH): Carboxylic acids
• Aldehyde group (-CHO): Aldehydes
• Ketone group (>C=O): Ketones
• Amino group (-NH�): Amines
• Halogen group (-X): Haloalkanes

Exercise 10.6

Question 7: Give the common name and IUPAC name of the following: (a) CH�Cl (b) CH�CH�Cl (c) CH�CHCl� (d) CH�CH�CH�Cl

Solution:

(a) CH�Cl
   - Common name: Methyl chloride
   - IUPAC name: Chloromethane

(b) CH�CH�Cl
   - Common name: Ethyl chloride
   - IUPAC name: Chloroethane

(c) CH�CHCl�
   - Common name: Ethylidene chloride
   - IUPAC name: 1,1-Dichloroethane

(d) CH�CH�CH�Cl
   - Common name: n-Propyl chloride
   - IUPAC name: 1-Chloropropane

JEE/NEET Focus Areas

Important Concepts for JEE

1. Hybridisation and Geometry: Understanding molecular geometry based on hybridisation
2. IUPAC Nomenclature: Systematic naming of organic compounds
3. Isomerism: Chain, position, functional group, and metamerism
4. Resonance: Delocalization of electrons in organic molecules
5. Inductive and Electromeric Effects: Electronic effects in organic compounds

Key Points for NEET

1. Recognition of Functional Groups: Essential for classification
2. Basic Organic Reactions: Addition, substitution, elimination reactions
3. Homologous Series: Understanding trends in properties
4. Organic Chemistry Basics: Foundation for complex mechanisms
5. Simple Reaction Mechanisms: Electron flow and bond making/breaking

Practice Questions

JEE Level Questions

Question 1: Which of the following compounds shows both sp� and sp� hybridisation?

Options: (A) C�H� (B) C�H� (C) C�H� (D) C�H��

Solution:

Let's analyze each option:

(A) C�H� (Ethene):
   H�C=CH�
   Both carbons are sp� hybridised

(B) C�H� (Acetylene):
   HCaCH
   Both carbons are sp hybridised

(C) C�H� (Propene):
   CH�=CH-CH�
   Terminal carbon = sp�
   Middle carbon = sp�
   Internal carbon = sp�
   Shows both sp� and sp� hybridisation 

(D) C�H�� (Butane):
   All carbons are sp� hybridised

Answer: (C) C�H�

Question 2: The number of stereoisomers possible for 2,3-dimethylbutane is:

Options: (A) 1 (B) 2 (C) 3 (D) 4

Solution:

2,3-dimethylbutane structure:
      CH�
       |
CH�-C-CH�
       |
      CH�

Analysis:
- The molecule has a plane of symmetry
- It does not show stereoisomerism
- Only one isomer exists

Answer: (A) 1

NEET Level Questions

Question 3: Which of the following functional groups is present in CH�COCH�Cl?

Options: (A) Aldehyde (B) Ketone (C) Alcohol (D) Ether

Solution:

CH�-CO-CH�Cl
    |
    C=O group

The functional group is the carbonyl group (>C=O) present in ketones.
Since the carbonyl carbon is attached to two carbon atoms, it's a ketone.

Answer: (B) Ketone

Question 4: The IUPAC name of CH�CH�CHClCH� is:

Options: (A) 1-Chlorobutane (B) 2-Chlorobutane (C) 3-Chlorobutane (D) 4-Chlorobutane

Solution:

CH�-CH�-CHCl-CH�
   1   2   3    4

Number from either end to give the substituent the lowest number:
- If numbered from left: 3-Chlorobutane
- If numbered from right: 2-Chlorobutane

Choose the lower number: 2

Answer: (B) 2-Chlorobutane

Memory Aids and Shortcuts

IUPAC Nomenclature Rules

1. Identify the longest chain
2. Number from the end giving substituents lowest numbers
3. Name substituents alphabetically
4. Indicate positions of multiple substituents

Hybridisation Mnemonics

sp hybridisation = 180� (straight line)
sp� hybridisation = 120� (planar triangle)
sp� hybridisation = 109.5� (tetrahedral)

Functional Group Priority Order

1. Carboxylic acid (-COOH)
2. Anhydride (-COO-CO-)
3. Ester (-COO-)
4. Acid halide (-COX)
5. Aldehyde (-CHO)
6. Ketone (>C=O)
7. Alcohol (-OH)
8. Amine (-NH�)
9. Ether (-O-)
10. Alkene (C=C)
11. Alkyne (CaC)
12. Alkane (C-C)

Common Mistakes to Avoid

1. Incorrect Numbering: Always number to give substituents lowest possible numbers
2. Wrong Functional Group Identification: Carefully examine the structure
3. Missing Isomers: Consider all types of isomerism
4. Hybridisation Errors: Count sigma and pi bonds correctly
5. IUPAC Naming Errors: Follow systematic rules strictly

Success Tips

1. Practice Structural Drawing: Draw clear, accurate structures
2. Master Functional Groups: Recognize them instantly
3. Understand Hybridisation: Connect structure with geometry
4. Learn IUPAC Rules: Practice naming regularly
5. Study Reaction Mechanisms: Understand electron flow

Master these fundamental organic chemistry concepts to build a strong foundation for advanced topics! >�

Remember: Organic chemistry is logical and systematic. Master the basics, and complex reactions will become easier to understand!

For additional practice, check out our Organic Chemistry Practice Problems and Video Lectures.