Class 11 Basic concept of organic chemistry Notes

Basic Concept of Organic Chemistry

Organic Chemistry:

The branch of chemistry which deals with organic compounds is called organic chemistry.

Organic Compounds:

Those compounds which are obtained from living organisms are called organic compounds.

Or,

Those compounds which are obtained from hydrocarbons and their derivatives are called organic compounds.

Vital Force Theory

(Information about vital force theory omitted)

Applications of Organic Compounds

• Food – Carbohydrate, Protein, Vitamin
• Shelter – Wood
• Clothing – Nylon, Cotton, Rayon
• Medicine – Paracetamol, Aspirin, Antibiotics
• Fertilizers – Urea (NH₂CONH₂)
• Fuel – Petrol
• Pesticides – DDT, BHC, Malathion
• Polymers – Polyethylene, PVC, Bakelite
• Cosmetics – Cream
• Explosive substances – TNT, Nitroglycerin
• Soap & Detergent

Tetravalency of Carbon

Carbon consists of four valence electrons in its outermost shell and shows tetravalency. Carbon forms covalent bonds by sharing valence electrons.

Catenation

The property of a carbon atom to form long chains of itself is called catenation.

For example:

  HHH                        HH
 H   C   C   C   C   C   H
 H   H   H   H   H   H
 Hexane

Classification of organic compounds

• Aliphatic Hydrocarbons: These are hydrocarbons in which the carbon atoms are linked in straight or branched chains. The table further divides aliphatic hydrocarbons into three subcategories:
  • Alkanes: These are hydrocarbons that have only single bonds between the carbon atoms. An example of an alkane is ethane (CH3CH3).
  • Alkenes: These are hydrocarbons that have one double bond between two carbon atoms. An example of an alkene is ethene (CH2=CH2).
  • Alkynes: These are hydrocarbons that have one triple bond between two carbon atoms. An example of an alkyne is ethyne (CCH=CH).
• Cyclic Hydrocarbons: These are hydrocarbons that have carbon atoms arranged in rings. The table divides cyclic hydrocarbons into two subcategories:
  • Homocyclic hydrocarbons: These are cyclic hydrocarbons that contain only carbon atoms in the ring. An example of a homocyclic hydrocarbon is cyclohexane.
  • Heterocyclic hydrocarbons: These are cyclic hydrocarbons that contain atoms other than carbon in the ring. An example of a heterocyclic hydrocarbon is pyridine.

Cyclic Hydrocarbons

Cyclic hydrocarbons are those hydrocarbons in which the carbon atoms are arranged in the form of a ring or closed chain. These can be further classified into two main categories:

1. Homocyclic Hydrocarbons: These are cyclic hydrocarbons which contain only carbon atoms in the ring.

• Examples:
  • Cyclopropane (C₃H₆)
  • Cyclohexane (C₆H₁₂)
  • Cyclooctane (C₈H₁₈)

2. Heterocyclic Hydrocarbons: These are cyclic hydrocarbons which contain atoms other than carbon atoms in the ring, along with carbon atoms.

• Examples:
  • Furan (C₄H₄O)
  • Pyrrole (C₄H₅N)

Cyclic Hydrocarbons

Cyclic Hydrocarbons are those hydrocarbons in which the Carbon atoms are arranged in the form of a ring or closed chain. These can be further classified into two main categories:

1. Homocyclic Hydrocarbons – These are cyclic hydrocarbons which contain only Carbon atoms in the ring.

• Examples:
  • Cyclopropane (C₃H₆)
  • Cyclohexane (C₆H₁₂)
  • Cyclo Octane (C₈H₁₈)

2. Heterocyclic Hydrocarbons – These are cyclic hydrocarbons which contain atoms other than Carbon atoms in the ring along with Carbon atoms.

• Examples:
  • Furan (C₄H₄O)
  • Pyrrole (C₄H₅N)

Functional Group

The most reactive part of an organic compound is called the functional group. The functional group determines the overall properties of the compound.

Some Important Functional Groups

Aldehydes and Ketones

• Aldehydes are carbonyl compounds in which the carbonyl group is located at a primary carbon atom (C-H).
• Ketones are carbonyl compounds in which the carbonyl group is located between two secondary carbon atoms (C-C).

Preparation

1. Primary alcohols can be oxidized by oxidizing agents like potassium dichromate (K₂Cr₂O₇) or potassium permanganate (KMnO₄) in acidic medium to form aldehydes.

Naming

• Aldehydes: The suffix -anal is added to the root name of the corresponding alkane.
• Ketones: The position of the carbonyl group is indicated by a number, followed by word “oxo” and then the root names of the two alkyl groups attached to the carbonyl carbon, linked by a hyphen. If the alkyl groups are identical, the prefix “di” is used before the root name.

Structure and Nomenclature

Examples

• Ethanal (CH₃CHO)
• Propanone (CH₃COCH₃)
• Butanal (CH₃CH₂CH₂CHO)
• 2-Pentanone (CH₃CH₂COCH₂CH₃)
• Phenylethanal (C₆H₅CH₂CHO) [Ph is used as an abbreviation for the phenyl group (C₆H₅)]

Carboxylic Acids

• A carboxylic acid is an organic compound containing a carboxyl group (COOH) attached to a hydrocarbon group.

Structure

• R-COOH (where R is the hydrocarbon group)

General Properties

• Carboxylic acids are sour in taste. [acetic acid = vinegar]
• They are soluble in water due to hydrogen bonding.
• They react with bases (alkali) to form salts.

Preparation

1. Oxidation of primary alcohols by strong oxidizing agents like potassium permanganate (KMnO₄) in acidic or alkaline medium.

Naming

• The suffix -oic acid is added to the root name of the corresponding alkane.
• If the carboxyl group is attached to a carbon atom in a ring, the word “carboxylic” is used instead of “oic acid”.

Examples

• Methanoic acid (HCOOH)
• Ethanoic acid (CH₃COOH) [acetic acid]
• Propanoic acid (CH₃CH₂COOH)
• Benzoic acid (C₆H₅COOH)

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Carboxylic Acids

• A carboxylic acid is an organic compound containing a carboxyl group (COOH) attached to a hydrocarbon group.

Structure

• R-COOH (where R is the hydrocarbon group)

General Properties

• Carboxylic acids are sour in taste. [acetic acid = vinegar]
• They are soluble in water due to hydrogen bonding.
• They react with bases (alkali) to form salts.

Preparation

1. Oxidation of primary alcohols by strong oxidizing agents like potassium permanganate (KMnO₄) in acidic or alkaline medium.

Naming

• The suffix -oic acid is added to the root name of the corresponding alkane.
• If the carboxyl group is attached to a carbon atom in a ring, the word “carboxylic” is used instead of “oic acid”.

Examples

• Methanoic acid (HCOOH)
• Ethanoic acid (CH₃COOH) [acetic acid]
• Propanoic acid (CH₃CH₂COOH)
• Benzoic acid (C₆H₅COOH) ░

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Esters

• Esters are organic compounds derived from carboxylic acids by replacing the hydrogen atom of the carboxyl group (-COOH) with an alkyl group.
• RCOOR’ (where R is an alkyl group and R’ is an alkyl or aryl group)

Preparation

1. Reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst like concentrated sulfuric acid (H₂SO₄).

Naming

• The name of an ester is formed by naming the alkyl group bonded to the oxygen atom (alkyl + the word “oate”) followed by the name of the acid from which it is derived.

Examples

• Methyl methanoate (HCOOCH₃)
• Ethyl ethanoate (CH₃COOCH₂CH₃) [ethylacetate]
• Phenyl propanoate (C₆H₅CH₂COOCH₂CH₂CH₃)