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 compounds	General formula
Alkane	CnH2n+2
Alkene	CnH2n
Alkyne	CnH2n-2
Alkanols	CnH2n+1OH/ROH
Alkanoic acid/carboxylic acid	Cn-1H2n-1COOH/RCOOH
Alkanoates /Esters	CnH2n+1COOCnH2n+1/RCOOR
Alkanals	CnH2n+1CHO/RCHO
Alkanones/Ketones	CnH2nCOCnH2n/RCOR
Ethers	CnH2n+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)

ALKANES

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.

Solution

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.

Solution

 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

Example

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

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 + 6H₂O 

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

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 + AgNO₃  à 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 + AgNO₃  à 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

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.

Hint

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

CH₃CHO + [O] –> CH₃COOH

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

CH₃CH₂COOH + CH₃OH –> CH₃CH₂COOCH₃ + H₂O

CH₃COOH + CH₃CH₂OH –> CH₃COOCH₂CH₃ + H₂O

CH₃CH₂COOH + CH₃CH₂OH –> CH₃CH₂COOCH₂CH₃ + H₂O

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

ALKANOIC ACIDS

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