CHAPTER-11

CHEMISTRY SSC-II                                      CHAPTER-11

Organic Chemistry

LECTURE# 1 

Organic chemistry :The Study of Carbon containing compounds and their properties is called organic chemistry. A detailed study of organic compounds confirms that carbon is an essential constituent in combination with H, O, N, S, P and halogens.

or

The branch of chemistry which deals with the study of hydrocarbons and their derivatives is known as organic chemistry

Catenation: Carbon’s ability to bond to each other to form long chains and rings. This self-linking ability of carbon is called catenation.

Isomerism.The compounds that have same molecular formula but different arrangement of atoms in their molecules are called isomers. This phenomenon is called isomerism.

For example two compounds have molecular formula C5 H12

General Characteristics of Organic Compounds

(i)Occurrence:Most of them come from living things or from the things that were once living.

(ii) Covalent nature:Organic compounds are generally covalent in nature. They may have polar or non-polar bonds.

(ii) Composition:

            Carbon is the main constituent of organic compounds. Hydrogen is also frequently present in organic compounds. Other elements like oxygen, nitrogen, sulphur, phosphorous and halogens are present in many organic compounds.

(iv) Melting and boiling point:

            Generally organic compounds are volatile. So they have low melting and boiling points.

(v) Solubility:

            Organic compounds are non-polar in nature; therefore mostly they are soluble in organic solvents such as ether, benzene, carbon disulphide etc. Polar Organic Compounds are soluble in alcohols such as methyl alcohol and ethyl alcohol.

(vi) Similarity in behaviors (Homology):

            There exists a close relationship between different organic compounds. This similarity in behavior has made the study of millions of organic compounds easier. They can be classified into few families. A series of related compounds in which any two adjacent molecules differ by –CH2– group is called homologous series.

(vii) Reaction rates:

            Organic compounds are generally less stable than inorganic compounds. Due to covalent bonding in them, their reaction rates are often slow.

(i) Molecular Formula

The formula which represents the actual number of atoms in one molecule of the organic compound is called the molecular formula, e.g., molecular formula of butane is C4H10. It shows:

Butane is made up of carbon and hydrogen atoms.Each molecule of butane consists of 4 carbon atoms and 10 hydrogen atoms.

(ii) Structural Formula

Structural formula of a compound represents the exact arrangement of the different atoms of various elements present in a molecule of a substance.

In a structural formula, single bond is represented by a single line (-), a double bond by two lines (=) and a triple bond by three lines ( ) between the bonded atoms.

Organic compounds may have same molecular formulae but different structural formulae, e.g., structural formulae of butane C4H10 are:

(iii) Condensed Formula

The formula that indicates the group of atoms joined together to each carbon atom in a straight chain or a branched chain is called the condensed formula.

(iv) Electronic or Dot and Cross Formula

The formula which shows the sharing of electrons between various atoms in one molecule of the organic compound is called dot and cross formula or electronic formula.

Saturated and Unsaturated Hydrocarbons

Saturated Hydrocarbons: whose carbon – carbon bonds are all single bonds are called saturated. Alkanes are types of saturated hydrocarbons.

Unsaturated Hydrocarbons: Hydrocarbons containing carbon-carbon multiple bonds are called unsaturated. Alkenes and Alkynes are types of unsaturated hydrocarbons.

  • Alkanes:

Saturated hydrocarbons containing  carbon-carbon single bond are called alkanes. They have general formula CnH2n+2, for example ethane.

  • Alkenes

Unsaturated hydrocarbons containing at least one carbon-carbon double bond are called alkenes. They have general formula CnH2n, for example ethene.

  • Alkynes
               Unsaturated hydrocarbons that have at least one carbon-carbon triple bond are called alkynes. They have general formula CnH2n-2, for example ethyne.

Naming Alkanes/ IUPAC METHOD

An international body, the international union of pure and applied chemistry (IUPAC) has devised a system of naming organic compounds that depends on their structure. These names indicate the number of carbon atoms present in the organic compounds. We can easily recognize organic compound by its IUPAC name. Such names are also called systematic names.

The IUPAC name has two parts.

(i) Stem:The stem tells the number of carbon atoms in the chain.

(ii)        Suffix:

            Suffix is placed after the stem, it tells the class of compound. For alkane, the suffix “ane” is used.

                                    Suffix it indicates alkane

                 Butane

                        Stem, it indicate no of carbon atoms stem

Q: What are Sources of Organic Compounds:

The major commercial sources of alkanes are coal, natural gas, petroleum, and living organisms.

  1. Coal:

Coal is blackish, complex mixture of compounds of carbon, hydrogen and oxygen. It also consists of small amounts of nitrogen and sulphur compounds.

Coal was formed by the decomposition of dead plants buried under the Earth’s crust millions of years ago. Conversion of wood into coal is called carbonization. It is a very slow biochemical process.

Coal has become a major source of organic compounds because of destructive distillation. The strong heating of coal in the absence of air is called destructive distillation.

  1. Coal gas contains methane, hydrogen and carbon monoxide gases. It is mainly used as a fuel in industry.
  2. Coal tar is a source of many organic compounds such as benzene and its derivatives. These compounds can be separated by fractional distillation. These are very useful substances in synthetic organic chemistry. These are used to synthesize plastics, dyes, fibers, drugs, paints, varnishes etc. The residue left behind called pitch is used to metal roads and roofs.
  3.  Coke is 98% carbon. It is left behind residue of coal. When coal is subjected to destructive distillation, it loses all its volatile components and leaves behind a solid residue called coke. It is mainly used as a reducing agent in the extraction of metals especially iron. It is also used as fuel.
  4. Natural gas

              Natural gas is a mixture of low boiling hydrocarbons. Natural gas is mostly methane. It also contains smaller amounts of ethane, propane and butane.

  • Petroleum

Petroleum is a dark brownish or greenish black coloured viscous liquid. It is a complex mixture of several solid, liquid or gaseous hydrocarbons in water mixed with salts and earth particles. Petroleum is a main source of organic compounds. It consists of several

Compounds mainly hydrocarbons. These compounds are separated by fractional distillation (separation of fractions or components depending upon their boiling point ranges)..

  • Living Organisms :Many important organic compounds such as proteins, fats, carbohydrates, vitamins, drugs and medicines are obtained from plants and animals.
  • Synthesis in Laboratory:

            Over ten million organic compounds have been prepared in the laboratories. They are being used in medicines, cosmetics, paints, plastics, fertilizer, detergents, etc.

Q: What are uses of organic compounds?

Uses of Organic Compounds.

  • Natural gas and petroleum are used primarily as fuel. These are also used as starting materials for the productions of variety of organic compounds.
  • Propane and butane which are gases obtained from natural gas are widely available as liquids in fuel cylinders (LPG).
  • Ethylene is the major starting material for the manufacture of organic chemicals and products such as polyethylene (plastic), ethyl alcohol, acetic acid and ethylene glycol called antifreeze.
  • Acetylene is widely used in the oxy-acetylene welding and cutting metals, Acetylene is also used in the preparation of polymers like PVC (polyvinyl chloride), polyvinyl acetate, synthetic rubber, nylon etc.
  • Acetylene is used for artificial ripening of fruits.
  • Compounds of phenol help to ensure antiseptic conditions in hospital operating rooms.
  • Methanol is used as a solvent for fats, oils, paints and varnishes.
  • Many organic compounds are used in the manufacture of drugs, dyes, cosmetics, detergents and soaps, nylon, emulsions and paints etc.
Self-Assessment Exercise 11.4
  1. List the names of major sources of alkanes.
  • What is natural gas?                                  3. Write some uses of acetylene.

Q: What is an alkyl radical?

Alkyl radicals: An alkane is a hydrocarbon containing only single bonds and have general formula CnH2n + 2.

  An alkyl radical is a group of atoms obtained by removing one hydrogen atom from an alkane. Alkyl radicals are represented by the symbol R. Their general formula is CnH2n+1

Q: How organic compounds are classified?

Organic Compounds  are broadly classified into two main groups.

  • Open chain compounds or Acyclic compounds.
  • Closed chain or Cyclic Compounds.
  1.  Open chain or Acyclic compounds

Open chain compounds are those in which the end carbon atoms are not joined with each other, in this way they form a long chain of carbon atoms. These chains may be either straight or branched. For example,

(a) Straight chain compounds are those in which carbon atoms link with each other through a single, double or triple bonds forming a straight chain such as;

b) Branched chain compounds are those in which there is a branch along a straight chain, such as:

 Open chain compounds are also called aliphatic compounds.

  • Closed chain or Cyclic compounds

Closed chain or cyclic compounds are those in which the carbon atoms at the end of the chain are not free. They are linked to form a ring. They are further divided into two classes:

Homocyclic or carbocyclic compounds.

Heterocyclic compounds.

(a) Homocyclic or Carbocyclic compounds.

Homocyclic or carbocyclic compounds contain rings which are made up of only one kind of atoms, i.e., carbon atoms. These are further divided into two classes:

Aromatic compounds

Alicyclic compounds

Aromatic compounds:

These organic compounds contain at least one benzene ring in their molecule. A benzene ring is made up of six carbon atoms with three alternating double bonds. They are called aromatic because of aroma or smell they have. For example:

Alicyclic compounds:

Carbocyclic compounds which do not have benzene ring in their molecules are called alicyclic compounds. For example

 Heterocyclic compounds

Cyclic compounds that contain one or more atoms other than that of carbon atoms in their rings are called heterocyclic compounds.

Functional Groups: An atom or groups of atoms that give a family of organic compounds its characteristic chemical and physical properties is called a functional group.

(i) Alcoholic Group

The functional group of alcohol is -OH. Their general formula is ROH. Where R is any alkyl group.

Phenols

OH
or
C6
 
H5
 _
OH
Phenol

            When an – OH group is attached to a benzene ring, the compound is called a phenol.

Phenol was the first antiseptic used in an operation theatre.

(ii) Ether Linkage

            Organic compounds that have two alkyl groups attached to the same oxygen atom are called ethers. These compounds have C–O–C linkage in their molecules.

CH3 – O – CH3    CH3 – O – CH2–CH3           

Dimethyl ether              Ethyl methyl ether 

CH3 – CH2 –O – CH2 –CH3  Diethyl ether

The general formula for ethers is R-O-R/. Where R and R/ are alkyl groups which may be same or different.

(iii)Aldehydes and ketones

                        Aldehydes and ketones contain the carbonyl group

                                       O            

                                                –C –      or       – CO –

  • An aldehyde has at least one hydrogen atom or two hydrogen atoms attached to the carbonyl carbon atom.
  •  A ketone has two hydrocarbon groups (alkyl) bonded to the carbonyl carbon atom.

Carboxylic Acids:

The functional group of organic acid is called the carboxyl group.

The general formula for carboxylic acids is R – COOH or R –C – OH.

ESTERS: Organic compounds consisting of RCOOR’ functional group are called esters.

R and R’are alkyl groups. They may be same or different, such as:

AMINES: The organic compounds containing carbon, hydrogen and nitrogen as functional group are called as amines. Their functional group is -NH2 and their general formula is R-NH2.

 Examples of amines are

EXERCISE

2.         Give short answer.

            (i)         What is catenation?

            (ii)        Define isomerism.

  • Give three examples of alkyl groups.

            (iv)      Define a functional group.

(v)       What is the difference between an alkane and an alkyl radical?

3.         What do you mean by the term destructive distillation?

4.         List some general properties of organic compounds.

5.         List major commercial sources of alkanes.

6.         Identify the following compounds on the basis of functional groups they contain and encircle the functional group.

            CH3 – CH = CH3                   ,           CH3 – C  CH          ,           CH3 – CH2 – COOH

                       O                                  ,                      O                      ,                       O                      

CH3 – C – OH                                   CH3 – C – CH3                             CH3 – C — OCH3

                   O

             H – C – CH3

7.         What is the name of alkane having seven carbon atoms in the chain?

8.         What is the name of the alkyl group obtained by removing an end hydrogen atom           from (i) propane (ii) ethane?

9.         Give the structural formula of two simple alkanes and one alkyne.

10.       What ismeant by the term functional group?

11.       Identify the type of following compounds as an alcohol, aldehyde or ketone:

  • HCHO, which is used to manufacture polymers, such as urotropine which is used to treat urinary tract infection.
    • CH3COCH3, which is used in nail polish remover.
    • CH3CH2OH, which is used in the preparation of many organic substances such as plastics, cosmetics, tinctures etc. 
  1. Given a molecular formula of a compound containing C, H and O and single bonds. List all the possible functional groups this compound can have?
  2. Give the condensed structural formulas of the following compounds and classify each on the basis of functional group.

H         H         H

(a)       H   –    C   –    C   –    C – OH

                        H         H         H

                  H             H

(b)       H – C – O – C – H

                   H           H

  1. The diagram represents an organic compound that contains three different elements.
       X      X  

 

X  – Z  – X

       X      X  

 

What could be the compound?

a) Ethanoic acid       b) propene    c) Ehanol       d) propane.

15.       Polyvinyl chloride (PVC) is a polymer. It is used for making vinyl sheets, drainage pipes, wire insulation etc. It is obtained from vinyl chloride

    H                   H

C = C

    H                   Cl

            Classify Vinyl chloride as saturated or unsaturated compound.

16.       For each of the following, draw the structural formulas of a two–carbon compound containing the indicated functional group.

                        (a) alcohol     (b) aldehyde       (c) carboxylic acid      (d) alkene   

17.       Aspirin is a mild pain killer and fever reducer. It is manufactured from salicylic acid.

            Identify functional groups present in it and encircle them.

18.       General formula for alkane is CnH2n+2. What will be the general formula for alkyl radical?

19.       Water adds to ethene according to the following reaction

             CH2 = CH2    +  H2O                            CH3CH2OH

             Identify functional groups in the reactant and product molecules.