NCERT Class 11 Chemistry Chapter 13 Notes Hydrocarbons - Download PDF

Hydrocarbons are compounds that consist of carbon and hydrogen only. Have you ever wondered what the world looks like if fuel is not available? Fuel is required to provide a source of energy to vehicles, to cook food, or to generate electricity. If fuel is not available then it becomes difficult for us to carry on our day-to-day activities. Hydrocarbons play a very important role in our day-to-day lives as they serve as the primary source of energy. Petrol and Diesel are hydrocarbons that are used as fuel for vehicles, LPG is also a hydrocarbon that is used for cooking. Some of the important topics covered in this chapter are types of hydrocarbons, their properties, formation and reactions. Hydrocarbons are the simplest organic compounds which form the basis of many complex compounds.

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This Story also Contains

1. NCERT Class 11 Chapter 9 Notes
2. Alkanes
3. Alkenes
4. Isomerism
5. Alkynes
6. Aromatic Hydrocarbons
7. Aromaticity
8. Activating Groups and Deactivating Groups
9. Meta-Directing Groups
10. Most Important Questions of Class 11 Chemistry Chapter Hydrocarbons
11. Approach to Solve Questions of Class 11 Chemistry Chapter 9 Hydrocarbons
12. NCERT Class 11 Notes Chapter-Wise
13. Subject-Wise NCERT Solutions

Class 11 NCERT chapter 9 notes are designed by our subject experts to make learning simple, clear, and easy. Hydrocarbon notes are provided in a very comprehensive way which will help students clarify the concept. These notes will help students to prepare for their final exams and competitive exams like JJEE mains, NEET, BITSAT, etc. These notes also covers the basic equations as well as the substitution reactions which includes some name reactions, aromaticity, Huckle’s rule, preparation of benzene which is required for the deep knowledge to score good in the examination.

Also, students can refer,

NCERT Class 11 Chapter 9 Notes

Discussing the Main Terms Related to Hydrocarbon

• Hydrocarbon

Compounds formed with the help of carbon and hydrogen are known as Hydrocarbons.

a)Saturated hydrocarbon:

Saturated hydrocarbons are those that contain a single bond in between two carbon atoms. Example: methane

b)Unsaturated hydrocarbon:

The hydrocarbon with double or triple bonds other than single bond is so called unsaturated hydrocarbons. Example: ethyne, ethene.

c)Aromatic Hydrocarbon:

The aromatic hydrocarbon is defined as compounds of benzene and their derivatives.

Example: Benzene and Aniline.

d)Alicyclic compounds:

The cyclic ring only consisting of carbon atoms are called alicyclic compounds.

Example:

e)Heterocyclic compounds:

The cyclic ring of such compound is composed of carbon as well as other than carbon atom.

Example:

Alkanes

Simplest form of organic compound that are made up of carbon and hydrogen. Carbon atoms are made up of single bond; covalent. As the chain of carbon is composed of single bonds only so they are fully saturated hydrocarbons. This class of alkanes are chemically inert in nature, so they are called paraffins.

Nomenclature

We proceed further with steps to understand the IUPAC nomenclature or how to write the structural formula of different hydrocarbons.

Step1. First to identify the longest chain among all the carbon.

Step2. In the second step give number to the selected chain. Try to give the number from left to right. As this should also be in mind that lowest numbers attached to alkyl group comes first.

Step3. Identifying the alkyl group attached to main chain.

Step4. Finally writing the IUPAC names.

Newman Projections

Relative stability of conformations

The two forms, decide the stability and energy of the molecule. When the alkane(ethane) is present in a staggered form, maximum repulsion occurs, which creates minimum energy and maximum stability. Whereas in the eclipsed form of ethane ,the stability reduces as the electrons of carbon cloud and hydrogen clouds come closer and it possesses more energy than the staggered form, thus the stability in this form reduces.

Alkenes

The carbon that contains a double bond in it are alkene with the general formula C_nH_2n.

Points to remember while writing the formula for alkenes:

1. Two bonds are present here in alkenes in which one is sigma and other is pi bond.

2. The availability of number of electrons in alkenes are higher so they are more reactive than alkanes.

Nomenclature for alkenes

For writing the names of alkenes the same steps should be followed up which we studied in the earlier sections of nomenclature, where the parent or main chain is the longest one and indication of number started from one end.

If in case in one chain two or more double bonds are present than diene suffix should be used for it.

Isomerism

Basically, we go through different types of isomerism, some of which are listed below.

1. Structural Isomerism:

2. Geometrical Isomerism:

Alkynes

Alkynes are the chain of carbon having triple bonds with the general formulaCnH_2n-2.

An important member of the alkyne group of hydrocarbons is acetylene.

Points to remember while writing the formula for alkenes:

1. In this triple bond two of them are pi bonds and one is sigma bond.

2. Similar to alkenes, the pi electrons are found more, so they will go in addition reaction.

Nomenclature for Alkynes:

For writing the names of alkenes the same steps should be followed up which we studied in the earlier sections of nomenclature, where the parent or main chain is the longest one and indication of number started from one end.

While writing the names of alkyne hydrocarbon we use suffix as yne and first numbering the carbon which is attached to triple bond.

Preparation of alkynes:

From calcium carbide: By treating calcium carbide with water formation of ethyne can be possible.

From vicinal dihalides: Dehydrohalogenation occur alcoholic potassium

Aromatic Hydrocarbons

The important feature of aromatic hydrocarbon is that most of the compounds containing the benzene ring and are also called arenes. The compounds having benzene rings are called benzenoids and those who have to benzene ring in their structure are termed as non-benzenoids.

Above mentioned are the examples of Hydrocarbon.

Nomenclature of Aromatic compounds

The common names according to IUPAC are accepted for naming the benzene and its homologous.

Structure of benzene:

The molecular formula of benzene is C6H6, and are highly unsaturated compound.

According to Kekule’s , he had given benzene structure in the year1865, in that he showed single and double bonds are present on alternate positions in the ring.

He also gave that the benzene ring would present in two forms.

Failures of Kekule’s benzene ring:

He wont able to explain how the stability of benzene ring can be achieved and also why the substitution reactions are preferred than addition reactions.

Resonance structure:

Resonance is defined as the where we can make two or more structures for the same compound and the atoms in that are also identical such structure is termed as Resonance structure.

Below showing you the resonance structure of benzene.

Orbital structure:

S-orbitals of hydrogen atom in Benzene ring form sigma bonds with carbon in condition of overlapping of hybrid orbitals.

Important points to remember:

• Benzene is found as planar in structure and this can be detected by the technique called X-ray diffractions.

• The bond length of carbon-carbon (139) which is intermediated between C-C of bond length(133pm) and C-C of bond length (154) is of same bond order. So, under normal benzene will go for addition reactions, which is the unusual behaviour of benzene.

Aromaticity

This is the property of sp² hybridized planar rings, where p orbitals allow cyclic delocalization of pi electrons.

Huckle’s Rule:

When cyclic pi electron cloud overlap, with p orbitals which contains(4n+2) pi electrons, such rule is termed as Huckle rule. Here n denotes the positive integer and 0.

Preparation of Benzene using different methods and compounds:

• It can be prepared commercially by isolating coal tar.

• There are some of the synthetic methods through which we can prepare the benzene.

• The synthetic methods are listed below:

Physical Properties

• Colourless liquid.

• Insoluble in water.

• Soluble in alcohol, ether, etc.

• Good solvent for organic and inorganic substances.

• Sooty flame with blue in colour.

Chemical Properties

• To show the chemical properties of benzene it must go through some reactions.

• Addition reaction

• Electrophilic substitution reaction

• Synthetic Methods:

Electrophilic Substitution Reactions is as Follows

Friedel-Crafts Alkylation Reaction

Mechanism Related to Electrophilic Substitution Reaction:

Steps included in the mechanism of electrophilic substitution reactions:

Step 1: In the first step formation of electrophiles occurs.

Step 2: To form the carbonium ion electrophile needs to attack the aromatic ring.

Step 3: Loss in a number of protons gives us the substitution product.

Carcinogenicity and Toxicity

Some of the polynuclear hydrocarbons contain benzene rings more than two in their chains, and when they fuse together they produce property that creates cancer.

They are formed by the incomplete combustion of tobacco, coal, etc.

Examples are as follows:

Activating Groups and Deactivating Groups

The activating groups are those who activate the benzene ring to attack with the help of an electrophile.

Deactivating groups are those who due to strong -I effect are formed which decreases the overall density and makes substitution difficult.

Meta-Directing Groups

These are the groups who helps to direct the incoming group to meta position are termed as meta-directing groups.

Most Important Questions of Class 11 Chemistry Chapter Hydrocarbons

Question 1: Benzene is treated with oleum to produce compound (X) which when further heated with molten sodium hydroxide followed by acidification produces compound (Y).The compound Y is treated with zinc metal to produce compound (Z).

Identify the structure of compound (Z) from the following option.

Answer:

Hence, the correct answer is option (2).

Question 2: Which compound would give 3-methyl-6-oxoheptanal upon ozonolysis ?

Answer:

3-methyl-6-oxoheptanal

Ozonolysis breaks the carbon–carbon double bonds in alkenes. Here, p-cymene undergoes ozonolysis, and the double bonds in the aromatic ring are cleaved. Each broken double bond is replaced by a carbonyl group (either an aldehyde or a ketone), resulting in a linear compound with aldehyde and ketone groups.

Hence, the correct answer is option (2).

Approach to Solve Questions of Class 11 Chemistry Chapter 9 Hydrocarbons

Alkanes, alkenes, alkynes and aromatic compounds are introduced along with their structures, classifications, and reactions in the chapter "Hydrocarbons." It is essential for Boards, NEET, and JEE and serves as a basis for organic chemistry. Here is a concise structured approach for students to follow

1. First focus on classification and nomenclature

   • Learning IUPAC naming for alkanes, alkenes, alkynes, and aromatic compounds is basic yet crucial step.

   • Also, try to learn about the structural features like bond types and hybridization.

2. Preparation methods and mechanisms of different compounds

   • Try to memorize key preparation reactions for each hydrocarbon type.

   • Learning the reaction mechanisms like free radical halogenation, electrophilic addition and substitution. is also important for the exams.

3. Learn physical and chemical properties

   • The trends in boiling point, solubility and reactivity are crucial to study.

   • Also, learn important tests - Baeyer’s test, bromine water test, etc.

4. Reactions of benzene and its derivatives

   • Try to grasp electrophilic aromatic substitution reactions (nitration, halogenation, sulfonation).

   • Also, study about directing effects and activating/deactivating groups.

5. Practice mechanism-based and conversion questions

   • Solve NCERT and previous year questions involving multi-step conversions.

   • Practice distinguishing tests, name reactions and mechanism reasoning (like Markovnikov’s/anti-Markovnikov’s rule).

Significance of NCERT Class 11 Chemistry Chapter 9 Notes

Hydrocarbons Class 11 notes, will help revise the chapter and covering the main topics more precisely and conveniently. The chemistry class 11 chapter 9 notes helps to understand the nomenclature and structures of different compounds. It will guide you to get a good score in the CBSE board examination

NCERT Class 11 Notes Chapter-Wise

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Subject-Wise NCERT Solutions