organic chemistry

What is Organic Chemistry?

Organic chemistry is the branch of chemistry that talks about the chemistry of carbon and its compounds.

The carbon element is not very abundant but it is very special because all organic matter like petrol, coal, animal,s etc contains carbon.

Carbon has the ability to combine with other carbon elements to form long chains, this property is called catenation.

Organic chemistry is classified and discussed under families called homologous series. There are various homologous series of organic compounds. There is a specific distinction for each homologous series, this is via functional groups.

Definition of Common Terms used in Organic Chemistry

  1. Hydrocarbons: Organic compounds that contain carbon and hydrogen only.
  2. Functional group: This is a bond, radical, atom or group of atoms specific to a homologous series and which determines the chemical property of the series.
  3. Isomerism: The existence of organic compounds with same molecular formula but different structural formula.
  4. Octane rating: The grading used in checking the quality of petrol.
  5. Cracking: This is the breaking down of hydrocarbons like alkanes into smaller hydrocarbons
  6. Reforming: This is the rearrangement of atoms in a compound to yield a getter quality hydrocarbon.
  7. Polymerization: This is the coming together of two smaller molecules called monomers to form heavy molecules called polymers.
  8. Saturated compounds: Saturated compounds are compounds that contain only single bonds.
  9. Unsaturated compounds: unsaturated compounds are compounds that contain double or triple bond.

Summary of the Homologous Series and their Functional Groups

Families of organic compoundsGeneral formula 
Alkanoic acid/carboxylic acidCn-1H2n-1COOH/RCOOH
Alkanoates /EstersCnH2n+1COOCnH2n+1/RCOOR
EthersCnH2n+1O CnH2n+1/ROR

Basic Facts in Organic Chemistry

  1. Hydrogenation of Alkenes yields alkanes
  2. Polymerization of ethene yields polyethene
  3. Polymerization of ethyne yields benzene
  4. Polymerization of benzene yields cyclohexane
  5. Hydrogenation of vegetable oil yields margarine/butter
  6. Hydration of alkenes yields alcohols/alkanaols
  7. Hydrolysis of alkenes yields alcohols/alkanols
  8. Oxidation of primary alkanols yields alkanoic/carboxylic acids
  9. Oxidation of secondary alkanols yields alkanones
  10. Oxidation of alkenes yields A diol (alkanol)
  11. Complete combustion of hydrocarbons yields carbon IV oxide and water
  12. Incomplete combustion of hydrocarbons yields carbon monoxide
  13. Dehydration of Alkanols yields alkenes
  14. Dehydration of sucrose/glucose yields soot (carbon)


Preparation of Alkanes

Alkanes are compounds that contain only single bonds. Alkanes undergo only combustion reactions, substitution reactions, and cracking reactions.

Combustion reactions

All hydrocarbons on complete combustion release carbon iv oxide and water

CH4 + 2O2 –> CO2 + 2H2O

2C2H6 + 14O2 –> 4CO2 + 6H2O

C3H8 + 3O2  –> 3CO2 + 4H2

simple problems on combustion reactions

Example 1

Calculate the volume of carbon IV oxide produced by the combustion of 3.3 moles of methane.


CH4 + 2O2 –> CO2 + 2H2O

1 mole of CH4 = I mole of CO2

3.3 moles of CH4 -X

     X = 3.3moles x 1 mole/ 1 mole

     X = 3.3 moles of CO2

 1 mole of CO2 = 22.4 dm3

 3.3 moles of CO2 = x

 X = 3.3 x 22.4

 X = 73.92 dm3

 Example 2

Consider the reaction;

C3H8 + 3O2  à 3CO2 + 4H2

If 24g of propane reacted, calculate the mass of hydrogen liberated.


 44g of propane à 132g

 24g of propane à x

  X = 24 x 132 /44

  X = 72g

Visit the link if you need more help or a guide on how to solve simple stoichiometry problems.

Substitution reactions

A substitution reaction is a reaction involving a direct displacement of an atom or group of atoms by another atom or group.

Alkanes undergo substitution reactions

CH4 + Cl2 –>CH3Cl + HCl

C2H6 + Cl2 –>C2H5Cl + HCl

C3H8 + Br2 –> C3H7Br+ HBr

These substitution reactions are phochemical

Cracking reactions

Alkanes are cracked to give smaller alkanes and alkenes. The cracking is a reaction specific to saturated hydrocarbons.

Please just remember that in cracking the model could be as follows;

Alkanes à smaller alkane + smaller alkene

Alkanes à smaller alkane + smaller alkene + another smaller alkene


C8H18 à C5H12 + C3H6

C8H18 à C3H8 + C3H6 + C2H4

IUPAC Nomenclature of Alkanes

I will show you some structures and nomenclature of some alkanes.


Alkenes are unsaturated hydrocarbons i.e they contain a double bond. Alkenes undergo combustion reactions, addition reactions, and polymerization reactions.

Combustion  reactions

Just like we said in the combustion of alkanes, carbon IV oxide, and water is also produced in the complete combustion of alkenes.

C2H4 + 3O2 –> 2CO2 + 2H2O

2C3H6 + 14O2 –> CO2 + 6H2

Addition reactions

Alkenes undergo addition reactions since it is unsaturated. Alkenes undergo addition reactions with halogens, hydrogen, and oxidizing agents.

An addition reaction involves the direct addition of an attacking reagent across the double or triple bond of an unsaturated compound to yield a single product.

  1. Addition of hydrogen(hydrogenation)

C2H4 + H2 –> C2H6

This is called hydrogenation

  • Addition of chlorine(halogenation)

C2H4 + Cl2 à C2H4Cl2

  • Addition of hydrohalides

C2H4 + HBr à C2H5Br

Polymerization reaction

The polymerization reaction is a type of reaction in which small molecules called monomers to combine to form large molecules called polymers. Polymerization reactions are of two types; addition polymerization and condensation polymerization.

Alkenes undergo polymerization to yield polymers. Polymers are plastics.

Examples of polymerization reactions

Polymerization of ethene

Ethene is polymerized into polyethene.

Other examples of polymerization reactions

Polymerization of chloroethene

Polymerization of propene


Alkynes are unsaturated hydrocarbons with triple bonds. Alkynes undergo combustion, addition, polymerization, and substitution reactions.

Combustion reactions

Alkynes can burn in oxygen to release carbon IV oxide and water.

  C2H2 + O2 –>2CO2 + H2O

  C3H4 + 4O2 –> 3CO2 + 2H2O

  C4H6 + 7/2 O2 — 4CO2 + 3H2O

Recall that there are stochiometry problems in combustion reactions.

Addition reactions

Many reagents can be added to alkynes to either form a less saturated hydrocarbon or an unsaturated hydrocarbon.

Addition of hydrogen –hydrogenation of alkynes

C2H2 + H2 –> C2H4

C2H2 + 2H2  –> C2H6

Addition of chlorine –halogenation of alkynes

C2H2 + Cl2 –> C2H2Cl2

Substitution reaction

Alkynes undergo substitution reactions with an ammoniacal solution of silver nitrate and copper I chloride.

C2H2 + AgNOà Ag2C2 + HNO3

C2H2 + 2CuCl –> Cu2C2 + HCl

How to differentiate saturated compounds (alkanes) from unsaturated compounds (alkenes/alkynes)

To differentiate unsaturated hydrocarbons from saturated hydrocarbons, you need aqueous bromine or bromine water.

Alkanes will not decolorize bromine water but alkenes and alkynes will decolorize bromine water.

How to differentiate alkenes from alkynes

To differentiate alkenes from alkynes, the two are unsaturated and both can decolourize bromine water.

We can use ammoniacal solutions of silver nitrateAgNO3 or ammoniacal solution of copper I chloride (CuCl).

Alkenes will not react with the ammonical solutions while alkynes will react with them.

C2H2 + AgNOà Ag2C2 + HNO3

Whitish yellow of silver dicarbide is observed

C2H2 + CuCl à Cu2C2 + HCl

The reddish-brown color of copper I dicarbide is observed


Alkanols or Alcohols are a set of homologous series that have the hydroxyl functional group (OH). They have the general formula R-OH but not hydrocarbons.

 Model ormula of alkanols

The general trend of alkanols is ROH

Where the R represents an alkyl

The members of alkanols are methanol, ethanol, propanol, butanol etc

The simplest member is the methanol.

   Members of alkanols and formula

   Methanol  – CH3OH

    Ethanol  -CH3CH2OH

Combustion reactions of Alkamols

Alkanols generally burn in oxygen to form carbon IV oxide and water.

Examples of combustion reactions of alkanols are shown below;

             2CH3OH + 3O2    –>  2CO2 + 4H2O

             C2H5OH + 3O2  –>  2CO2 + 3H2O

             2C3H7OH + 9O2  –> 6CO2  + 8H2O

             C4H9OH + 6O2  –>  4CO2 + 5H2O

Oxidation of alkanols

Alkanols can be oxidized by warming with strong oxidizing agents like acidified potassium heptaoxo dichromate VI solution.


Please take note that primary alkanols are oxidized completely to alkanoic acids and incompletely to alkanals.

Secondary alkanols/alcohols  are oxidized to ketones or alkanones

Tertiary alkanols/alcohols are never oxidized.

Mechanism of oxidation of alkanols

C2H5OH + [O] –> CH3CHO + H2O


Reaction with metals (like Sodium and Potassium)

Very electropositive metals like sodium can react with alcohol to form ethoxides and liberate hydrogen.

C2H5OH + Na –> C2H5ONa + H2    Sodium ethoxide formed

C2H5OH + K –> C2H5OK + H2       Potassium ethoxide formed

Esterification reaction

What is an Esterification reaction? An esterification reaction is a reaction between an alcohol and a carboxylic acid to form ester and water.

Alcohols react reversibly with carboxylic acids to form esters and water.

Examples of the esterification reaction




Dehydration of alkanols

Alkanols can be dehydrated at about 1700C in the presence of concentrated sulphuric acid to yield alkenes when aid in excess.

   C2H5OH  + H2SO2 –> C2H5HSO4 + H2O

   C2H5HSO4 –> C2H4 + H2SO4

Alkanols can be dehydrated at about 1700C in the presence of concentrated sulphuric acid but in excess, alkanols yield ether.

     C2H5OH + H2SO2 –> C2H5HSO4 + H2O

     C2H5HSO4 + C2H5OH –> C2H3OC2H5 + H2SO4


The alkanoic acids otherwise called carboxylic acids have the general formula of RCOOH  and they have the carboxyl functional group.

The members of alkanoic acid are methanoic ethanoic acids, propanoic acid, butanoic acids etc

Methanoic acid HCOOH, Ethanoic acid CH3COOH, Propanoic acid CH3CH2COOH etc

Alkanoic acid /carboxylic acids are weak acids and show some specific reactions.

Acidic properties of Carboxylic acids

  1. Alkanoic acids reacts with carbonats

2HCOOH + CaCO3 –> (HCOO)2Ca + H2O + CO2

2CH3COOH + MgCO3 –> (CH3COO)2Mg + H2O + CO2

  • Alkanoic acids react with electropositive metals (Mg, Na,K)

2CH3COOH + Mg –> (CH3COO)2Mg + H2

CH3COOH + K  –> CH3COOK + 2H2

  Alkanoic acids react with base (alkali)

              CH3COOH + NaOH –> CH3COONa + H2O

               CH3COOH + KOH –> CH3COOK + H2O

Esterification Reaction

   Carboxylic acids react with alkanols to form esters and water.

    CH3COOH + C2H5OH –> CH3COOC2H5 + H2O

Decarboxylation reaction

If alkanoic acid is heated strongly with soda lime, alkanes will be produced.

CH3CH2COOH –> C2H3 + CO2

CH3COOH –> CH4 + CO2

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