Organic Chemistry - Some Basic Principles and Techniques Class 11 Notes CBSE Chemistry Chapter 12 (Free PDF Download)

Section-A (1 Mark Questions)

1. Define homologous series

Ans. A group or a series of organic compounds each containing a characteristic functional group forms a homologous series and the members of the series are called homologues and the successive members differ from each other in molecular formula by a –CH2 unit.

2. Define carbanion.

Ans. A carbon species carrying a negative charge on carbon atom is called carbanion. Carbanions are also unstable and reactive species.

3. Give the reason for the fusion of an organic compound with sodium metal for testing nitrogen, sulphur and halogens.

Ans. The element present in the compound is converted from the covalent form into ionic form by fusing the compound with sodium metal.

4. Write the expanded form of the following condensed formulas into their complete structural formulas. 

(a) CH3CH2COCH2CH3.

(b) CH3CH = CH(CH2)3CH3.

Ans.

5. What is a functional group?

Ans. It may be defined as an atom or group joined in a specific manner that is responsible for the characteristic chemical properties of the organic compounds.

6. A species having a carbon atom possessing ………….. of electrons and a positive charge is called a carbocation.

Ans. sextext

7. Free radicals are formed due to ………….. bond fission.

Ans. homolytic

8. The Prussian blue colour obtained during Lassaigne’s test for nitrogen is due to the formation of ………

Ans. Ferric ferrocyanide

9. The different fractions of crude oil can be separated by

Ans. Fractional distillation

10. Inductive effect involves displacement of electrons (True/False).

Ans. True

Section-B (2 Marks Questions)

11. What are reactive intermediates? How are they generated by bond fission?

Ans. The reactive intermediates are those chemical species that are produced during the course of the reaction. There are many reactive intermediates, three of which are carbocation, carbanion and the free radical.

Carbocation and carbanion are generated by the heterolytic bond fission while free radicals are generated by homolytic bond fission.

12. Why does SO3 act as an electrophile?

Ans. In SO3, three highly electronegative oxygen atoms are attached to a sulphur atom. It makes sulphur atom electron deficient. Further, due to resonance, sulphur acquires a positive charge. both these factors, make SO3 an electrophile.

13. Write structural formulae for compounds named as

(a) 1-bromoheptane

(b) 5-bromoheptanoic acid

Ans.

14. Give the structure and hybridization of

I. CH3+

II. CH3–

Ans.

15. What is the type of hybridization of each carbon in the following compounds?

(a) CH3Cl

(b) HCONH2

Ans. (a) sp3

(b) sp2

16. Write the structural formula of:

(a) o-Ethylanisole 

(b) p-Nitroaniline

Ans.

17. Identify electrophilic centre in the following: 

CH3CH = O, CH3l.

Ans. Among $\text{CH}_3\text{H}\overset{*}{\text{C}}=\text{O},\text{H}_3\overset{*}{\text{C}}-1$ the starred carbon atoms are electrophilic centers as they will have partial positive charge due to polarity of the bond.

18. In which C–C bond of CH3CH2CH2Br, the inductive effect is expected to be the least?

Ans. Magnitude of inductive effect diminishes as the number of intervening bonds increases. Hence, the effect is least in the bond between carbon-3 and carbon-2.

19. What is the basic principle of Crystallization & Chromatography?

Ans. Principle of Crystallization : It is based on the difference in the solubility of the compound and the impurities in a suitable solvent.

Principle of chromatography: The technique of chromatography is based on the fact that different constituents of a mixture are adsorbed to different extents by given adsorbent.  The medium which carries the mixture of solvent (such as ether, benzene, alcohol etc.) is called a moving phase and the medium in which various components are adsorbed (such as alumina, silica get etc.) is called the stationary phase.

20. Write formulas for the next four members of homologous series for the compound, HCOOH.

Ans. CH3—COOH
CH3CH2—COOH  CH3CH2CH2—COOH
CH3CH2CH2CH2—COOH

PDF Summary - Class 11 Chemistry Organic Chemistry-Some Basic Principles & Techniques Notes (Chapter 7)

1. General Organic Chemistry

1.1 Introduction

Berzelius coined the term "Organic Chemistry" in 1807 to describe the study of compounds derived from natural sources. This was based on the vitalism theory, which stated that all living systems possessed a 'vital force' that non-living systems lacked. Organic compounds were thought to be fundamentally different from inorganic compounds because they were derived from living natural sources.

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Philosophically, the vital force could be thought of as the mysterious force that God instilled in living systems.

Friedrich Wohler became Berzelius' student in 1823. Wohler made a discovery in 1828 that changed the definition of organic chemistry. Wohler carried out the following experiment.

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Wohler was able to successfully synthesize an organic compound from an inorganic compound. Many others followed suit, synthesizing organic compounds from inorganic compounds. As a result, the theory of vitalism and the definition of organic chemistry became meaningless.

The presence of carbon, however, was shared by all of the compounds synthesized above. Catenation is a unique property of carbon. Carbon can form long chains and rings with other carbon atoms (self-catenation), as well as with atoms of many other elements in the periodic table (cross-catenation). As a result, carbon can form a wide range of compounds.

The vital force is probably explained by the fact that most of the life-giving and life-sustaining functions are performed by carbon compounds, for example, human tissues and skin are formed by proteins, respiration is possible because of hemoglobin, information in our genes is carried out in the form of DNA/RNA, and so on.

The detailed study of the fundamental concepts and factors that govern the progression and outcome of reactions is known as general organic chemistry.

Note:

Before transforming into products, bonds are typically formed and broken in a series of discrete steps. The mechanism of the reaction is a detailed sequential description of all the steps.

1.2 Sigma and Pi bond

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1.3 Structural Formulas

Organic chemists use a variety of formulas to represent organic compounds.

1.3.1 Complete Formulas

Lewis structures are used to represent all bond pairs of electrons as a dash (–) in complete formulas. A lone pair of electrons is represented by a pair of dots.

1.3.2 Condensed Formulas

Condensed formulas do not include all of the individual bonds. Each central atom is depicted, along with the atoms that are bonded to it.

1.3.3 Line-Angle Formulas

These are also referred to as skeletal structures or stick figures. Line-angle formulas are frequently used for cyclic compounds and, on rare occasions, non-cyclic compounds. Lines represent bonds, and carbon atoms are assumed to be present where two lines intersect or where a line begins or ends. In most cases, hydrogens are implied in these drawings.

1.3.4 Tetrahedral Representation

This is the three-dimensional (3-D) representation of molecules in general. Bonds projecting behind the plane (away from the observer) or out of the plane (towards the observer) are denoted by a dashed Wedge or a solid Wedge, respectively. Bonds in the plane of paper are represented by a normal line (—).

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2. Degrees of Carbon

It is defined as the number of carbons attached to the carbon under study.

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2.1 Hybridization

Hybridisation is a process in which two or more atomic orbitals of comparable energy in the valence-shell of an atom (central atom of a molecule or ion) mix together and give rise to the formation of new degenerate orbitals known as hybrid orbitals.

2.2 Applications of Hybridization

2.2.1 Size of Hybrid Orbitals

The size of the hybrid orbital decreases as the percentage of s-character increases. As a result, the size of the hybrid orbital is: sp3 > sp2 > sp.

2.2.2 Electronegativity of Hybrid Orbitals 

As the percentage of s-character increases, so does the electronegativity of the hybrid orbital. As a result, the EN of the Hybrid Orbital is sp > sp2 > sp3

2.3 Dienes

Dienes are organic compounds that have two double bonds in them. Dienes are classified into three types: Isolated, Conjugated and Cumulated

2.3.1 Isolated Diene

In this case, double bonds are separated by atleast one sp3 carbon.

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2.3.2 Conjugated Diene

A single bond separates two double bonds (or 4 sp2 carbons in a row).

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2.3.3 Cumulated Diene 

Both sets of double bonds are located on the same carbon atom.

$\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{C}=\mathrm{CH}-\mathrm{CH}_{3}$

2.3.4 Stability Diene

The relative stabilities of dienes are arranged in the following order: 

Isolated > Conjugated > Cumulated

2.4 Commonly occurring forms of carbon

Carbon's most common forms are 

(a) diamond, 

(b) graphite 

(c) carbides.

(d) Fullerenes

(e) Charcoal

Note:

Each C in a diamond is sp3. The solid is tetrahedral.

Each C in graphite is sp2. Solid layers with weak van der Waal forces between them. 

3. Breaking of Bonds:

The bond that is important for the study of reactions in organic chemistry is the covalent bond. As a result, we investigate how a covalent bond can be broken.

(a) Homolytic Fission 

(b) Fission by Heterolysis

3.1 Homolytic Fission or Homolytic Cleavage

Each atom separates with one electron in this type of bond breaking, resulting in the formation of highly reactive species known as radicals (or free radicals).

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Two half-headed or fishhook arrows represent bond breaking. One electron's movement is depicted by a half-headed arrow. Radicals are odd electron species that are neutral.

3.1 Heterolytic Fission or Homolytic Cleavage

The shared pair of electrons are transferred to the more electronegative part in this type of covalent bond breaking. As a result of this fission, a cation and an anion are formed (ion-pair).

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A full-headed arrow represents the bond breaking. A full-headed arrow depicts the movement of two electrons. In organic chemistry, electron movement is always represented by curved arrows, either half-headed or full-headed.

4. Inductive Effect:

When two unlike atoms form a covalent bond, the electron- pair that forms the sigma bond is never shared equally between the two atoms, but is shifted slightly towards the more electronegative species.

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As illustrated, there are three types of groups/atoms that can be attached to carbon. Although C is more electronegative than H, the difference in electronegativity is small, and the bond is generally considered non-polar.

4.1 Nature of Inductive Effect:

The inductive effect is a permanent effect that is directly proportional to the dipole moment. It is a minor effect because electrons are only shifted via sigma bonds.

4.2 Effect of Branched Carbon Chain

An example of the operation of the inductive effect has been marked, which is self-explanatory.

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4.3 Electron Donating and Electron withdrawing Groups 

The inductive effect can be caused by a single atom or by a group of atoms. The relative inductive effects are measured in relation to hydrogen. Electron-donating groups (EDG) or electron-releasing groups (ERG) are those that donate electrons to the carbon chain and are said to exert a +I effect. Electron-withdrawing groups (EWG) are those that withdraw electrons from the carbon chain and are said to exert the –I effect.

Important: 

1. I.E. of alkyl groups : 3° > 2° > 1° > CH3 – 

2. In general, the number of carbons in an alkyl group increases the +I effect.

3. To solve the problem, we assume that the electronegativity of sp hybridized carbon is greater than that of sp3 hybridized nitrogen.

4.4 Applications of Inductive Effect 

4.4.1 Effect on Acidic/Basic Strength 

EWG raises acidic strength while decreasing basic strength. ERG reduces acidic strength while increasing basic strength. 

Example: Compare the acidic strength:

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Solution: An alkyl group will only donate if no other EWG is present. As a result, electron withdrawing groups such as –CH2Cl and –CH2F form.

Order of Acidic Strength  III > II > I 

4.4.2 Effect of Distance 

The inductive effect decreases as the ERG/EWG moves away.

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4.4.3 Basicity of Amines 

The order in gaseous or liquid phase is: 3° > 2° > 1° > NH3 

To ascertain the basic strength of amines in aqueous solution. We must consider the inductive effect, the solvation effect, and the steric hinderance. The order of basic strength is thus experimental in the aqueous state because we cannot prioritize the stability provided by any single factor. For the aqueous phase, two results are critical: 

(a) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}>\mathrm{CH}_{3} \mathrm{NH}_{2}>\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}>\mathrm{NH} 3$

i.e. $2^{\circ}>1^{\circ}>3^{\circ}>\mathrm{NH}_{3}\left(\mathrm{R}=\mathrm{CH}_{3}\right)$

(b) $\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{NH}>\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{3} \mathrm{~N}>\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}>\mathrm{NH}_{3}$

i.e. $2^{\circ}>3^{\circ}>1^{\circ}>\mathrm{NH}_{3}\left(\mathrm{R}=\mathrm{C}_{2} \mathrm{H}_{5}\right)$

5. Resonance 

Simple Lewis structures are commonly used to represent molecules, but some molecules cannot be represented by a single Lewis structure. As a result, the concept of resonance was discovered. The delocalization of electrons (generally pi electrons) is referred to as resonance. 

5.1 Conjugated Systems 

5.1.1 Pi alternate Pi

5.1.2 Pi alternate Positive Charge 

Example - 4

5.1.3 Pi alternate Negative Charge 

Example - 5

5.1.4 Pi alternate Odd Electron 

Example - 6

5.1.5 Pi alternate Lone Pair 

Since lone pair and negative charge are treated similarly, this case is similar to 'pi alternate negative charge.

Example - 7

5.1.6 Lone Pair and Positive Charge on Adjacent Atoms 

Example - 8

5.2 Rules for Validity of Lewis Structures 

Rule 1: All Lewis structures must adhere to the Lewis octet rule.

Rule-2: Atoms in all resonating structures must be in the same position. Only the electrons are in motion.

Rule-3: All resonating structures must have the same number of paired and unpaired electrons, that is, the sum of bond pairs and lone pairs must be constant.

Rule-4: All of the atoms in a molecule that participate in resonance must be coplanar. This is required for effective p orbital overlap and electron delocalization, as in buta-1,3-diene.

5.3 Criteria for Major/Minor Contributors 

The following criteria, in the following order, can be used to compare resonance forms:

1. Use as many octets as you can (a neutral molecule is always more stable in which its octet is complete).

2. Attempt to form as many bonds as possible.

3. The presence of a negative charge on a more electronegative atom is stable.

4. The separation of charges

(a) Similar charges - Keep them as far away from each other as possible to reduce repulsion and instability.

(b) Opposite charges should be kept as close together as possible to maximize attraction and stability. 

Example - 9 

Which of the following structures is more stable?

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Solution: II is more stable as all the octets are complete. 

6. Mesomeric Effect 

The permanent polarization caused by a group conjugated with a pi bond or a set of alternate bonds is transmitted through the system's electrons, resulting in a different electron distribution in the unsaturated chain. Mesomeric Effect or Resonance Effect refers to the redistribution of electrons in unsaturated compounds conjugated with electron-releasing or electron-drawing groups (or atoms). The dipole moment indicates that this effect is permanent. 

6.1 Electron-Releasing and Electron-Withdrawing Groups 

The M or R effect refers to groups that release or withdraw electrons via resonance. 

6.1.1 Electron-Releasing Groups (+R or +M effect)

The atom connected with the conjugated system has a lone pair to donate, which is shared by all of the groups listed. As a result, a generic representation can be represented.

6.1.2 Electron-Withdrawing Groups (–R or –M effect)

All of the groups listed have one thing in common: the atom connected with the conjugated system has a bond with another more electronegative atom that either withdraws electrons or directly has a positive charge on them. As a result, a generic representation can be represented - Y=Z (ENZ > ENY) 

6.1.3 Dual Behaviour 

As shown, some groups are both electron-releasing and electron-drawing. 

Example - 12 

As electron releasing group

As electron withdrawing group

Which behaviour dominates and which is used in a particular context will be discussed later in Electrophilic Aromatic Substitution later. 

Resonance Effect does NOT depend upon distance unlike inductive effect. 

6.2 Applications of Mesomeric Effect 

6.2.1 Effect on Acidic Strength of Carboxylic Acids and Phenols 

The resonating structure of carboxylic acid results in a charge-separated structure that is less stable than the charge-delocalized carboxylate ion. As a result, carboxylic acid easily loses proton (H) to form a carboxylate ion.

Similarly, in phenol, resonance causes charge separation, which increases the rate of ionization and results in the formation of phenoxide ion, which is stabilized by charge delocalization.

6.2.2 Effect on Reactivity of Carboxylic Acid Derivatives 

A typical nucleophilic reaction is represented as : The stronger is the bond between C and Z, the more difficult it is for a nucleophile to break a bond and therefore, lower reactivity. Reactivity order of carboxylic acid derivatives towards nucleophilic acyl substitution is : Acyl Chloride > Acid Anhydride > Ester > Amide

6.2.3 Effect of ERG/EWG on Acidic/Basic Strength 

EWG increases the acidic strength and decreases the basic strength. ERG decreases the acidic strength and increases the acidic strength.

Some Basic Concepts of Organic Chemistry Class 11 Notes

Class 11 chemistry organic chemistry notes will help you to better understand the chapter. These notes are completely NCERT based and have been prepared by experts.

A General Introduction to Organic Chemistry - Class 11 Chemistry Chapter 12 Notes

Organic chemistry is the branch which studies carbon compounds obtained from living organisms. It is a very important discipline of chemical science.

Carbon exhibits a unique self-linking property to form chains, layers and space lattices. This property is known as catenation. Carbon also exhibits tetravalency which is satisfied by forming bonds with carbon, hydrogen and other atoms. Because of these properties, carbon is able to form a huge number of compounds.

Nomenclature According to IUPAC Rules

Nomenclature of organic compounds is done in accordance with the rules laid down by IUPAC which stands for the International Union of Pure and Applied Chemistry. This body formulates rules for the naming of Organic compounds. 

Certain Important Concepts of Organic Chemistry

• Functional Groups: Functional groups can be defined as an atom or a group of atoms which replace hydrogen in an organic compound.

• Homologous Series: Homologous series is a sequence of organic compounds having the same functional group and chemical properties in which the member of the series successively differ by - CH2

Organic Compounds and Their Classification

Organic compounds can be classified as given in chemistry Chapter 12 Class 11 notes :

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Isomerism

Isomerism in organic chemistry, as explained in the notes of Chapter 12 chemistry Class 11 can be of two types-

• Structural Isomerism: Structural Isomerism occurs due to different structural arrangement of atoms of a chemical compound with the same chemical formula. 

• Stereoisomerism: Stereoisomeric compounds have the same chemical formula and bond sequence but they have a different 3D orientation of atoms in space. Stereoisomerism is of two types- Geometrical Isomerism and Optical Isomerism.

Attacking Reagents 

The attacking reagents mentioned in notes of chemistry Class 11 Chapter 12 are as follows:

• Attacking Reagents are chemical species which bring about a chemical reaction. They may be electrophiles or nucleophiles. 

• Electrophiles: Species which accept electron pairs are known as electrophiles meaning ‘electron seeking’.

• Nucleophiles: Species which donate or provide electron pairs are known as nucleophiles meaning ‘nucleus seeking’. 

Reaction Intermediates of Class 11 Chapter 12 Chemistry Notes

Carbocations, Carbanions and Free Radicals are the reaction intermediates. 

• Carbocations: Carbocations are carbon intermediates with a positive charge and have six electrons in the valence shell. It has sp² hybridization.

• Carbanions: Carbanions are carbon intermediates with a negative charge. They have eight electrons in the outermost shell. Their hybridization is sp³.

• Free Radicals: Carbon-free radicals are intermediates with odd electrons. They are neutral and have seven electrons in the valence shell and have hybridization as sp².

Electron Displacement Effects in Covalent Bonds As Given in Chapter 12 Chemistry Class 11 Notes

Electron Displacement occurs in an organic compound either under the influence of an atom or substituent group in the ground state or in presence of a suitable attacking reagent. There are certain effects visible. These are-

• Inductive Effect: Bond formed between unlike species will have the electron pair shifted towards the more electronegative atom. This is known as Inductive Effect and this is a permanent effect.

• Resonance or Mesomeric Effect: When the structure of a molecule cannot be explained explicitly in a single Lewis dot structure then a number of structures are required to show the structure of the molecule. This occurs because of the delocalization of pi electrons. This is again a permanent effect.

• Hyperconjugation Effect: Hyperconjugation can be defined as the ability of the sigma bond electrons of an alpha-carbon to form conjugation with adjacent pie electrons. 

• Electromeric Effect: Electromeric effect is the shifting of electron pairs towards more electronegative atoms in a double-bonded system in presence of a reagent. This is a temporary effect.

Methods of Purification of Organic Compounds as Mentioned in Some Basic Concepts of Organic Chemistry Class 11 Notes

• Simple Crystallization: In this process, a solvent is selected for preparation of a solution in which one of the elements crystallizes out in the form of a compound.

• Sublimation: This process is used for purifying relatively volatile organic solids.

• Simple Distillation: In this process, a liquid is converted into vapour and the vapour is transferred to another place and recovered by condensation.

• Fractional Distillation: This process is used for purification of two substances with less difference in boiling points.

• Simple Distillation: In this process, a liquid is converted into vapour and the vapour is transferred to another place and recovered by condensation.

• Chromatography: In this process, the mixture is passed through a solution or suspension where it has different rates of moving. There are various types of chromatography like column chromatography, paper chromatography, etc.

Qualitative Analysis in Class 11 Chemistry Ch 12 Notes

From the qualitative analysis of organic compounds, we find out the elements present in the compounds in addition to carbon and hydrogen. There are various tests and methods for qualitative analysis of organic compounds. 

Quantitative Analysis in Ch 12 Chemistry Class 11 Notes

The Quantitative Analysis of an organic compound is the process by which the relative abundance, mass, or concentration of every single component is found out. This is important for the proper study of the compounds.  

Chapter 12 chemistry Class 11 notes are written precisely yet are enough for revision before the examination. It is very well curated in a systematic manner. 

The organic Chemistry Some Basic Principles and Techniques Class 11 notes is very important for the NEET and JEE aspirants as mentioned earlier. There have been important and conceptual questions from the chapter in the examinations.

Conclusion

In conclusion, the CBSE Class 11 Chemistry Chapter 12 notes on "Organic Chemistry - Some Basic Principles and Techniques" offer a valuable resource for students studying this topic. These notes provide a comprehensive overview of fundamental concepts and techniques related to organic chemistry. Topics covered include nomenclature, isomerism, functional groups, and various organic reactions. By studying these Class 11 notes, students can enhance their problem-solving skills, gain a deeper insight into organic chemistry, and prepare effectively for their examinations. They serve as a valuable aid for self-study, revision, and exam preparation.