O level Organic Chemistry brief study notes

Organic Chemistry Brief Notes by chong56 on Scribd

 

 

Alcohols

Introduction

• Alcohols are a family of organic compounds containing carbon , hydrogen and oxygen.

• The general formula of alcohols is C_nH_2n+1OH (n = 1, 2, 3, 4…)

• The reacting group (or functional group) is the hydroxyl group, -OH.

• The names of an alcohol end with –ol.

• Propanol has 2 isomers.

Formation of ethanol

• Ethanol is obtained by

• (a) fermentation

• (b) catalytic addition of steam to ethene

• (a) Fermentation breaks down the sugar into ethanol and carbon dioxide. Yeast is used as a catalyst.

_• C₆H₁₂O₆ --> 2C₂H₅OH + 2CO₂

sugar ethanol

Temperature of 37^oC is used. Temperature is important in fermentation.

• (b) Addition of steam to ethene at high temperature (300^oC) and pressure (67 atm) produces ethanol. Phosphoric acid is used as a catalyst.

• CH₂=CH₂ + H₂O --> CH₃-CH₂OH

Reactions of alcohols

• Alcohols undergo 3 important reactions:

• (a) Combustion

• (b) Oxidation

• (c) Esterification

Combustion of alcohols

• Alcohols burn in oxygen to produce carbon dioxide and water.

• C₂H₅OH + 3O₂ --> 2CO₂ + 3H₂O

Oxidation of alcohols

• Alcohols are oxidised to carboxylic acids.

• The number of carbon atoms remain the same in oxidation.

• CH₃CH₂OH + 2[O] --> CH₃COOH + H₂O

• The oxidation is carried out by using

• (i) oxygen

_• (ii) acidified K₂Cr₂O₇

_• (iii) acidified KMnO₄

Oxidation of alcohols

• During the oxidation:

– Acidified K₂Cr₂O₇ turns from orange to green

– acidified KMnO₄ is decolourised.

Esterification

• Alcohols react with organic acids to form esters. Esters are sweet fruity-smelling compounds.

• Word equation :

• Alcohol + carboxylic acid --> ester + water

Uses of ethanol

• As a solvent

• As a fuel

• As a constituent of wine and beer

• Human consumption of wine and beer can lead to alcohol addiction.

A model of an ethanol molecule

• Ethanol, C₂H₅OH, is used in beer making.

Carboxylic Acids

• Carboxylic acids are a family of organic compounds containing carbon, hydrogen and oxygen.

• The general formula of carboxylic acids is C_nH_2n+1COOH (n = 0, 1, 2, 3, 4…)

• The functional group is the –COOH group.

• Carboxylic acids end with –oic acid.

Carboxylic acid

• Butanoic acid has 2 isomers.

• Formation of ethanoic acid

– Ethanoic acid is formed by the oxidation of ethanol.

• By using atmospheric oxygen:

• CH₃CH₂OH + O₂ --> CH₃COOH + H₂O

• By using acidified K₂Cr₂O₇.

• CH₃CH₂OH + 2[O] à CH₃COOH + H₂O

• The orange dichromate (VI) solution changes from orange to green.

• A vinegar smell is detected.

Reactions of carboxylic acids

• Two important reactions of carboxylic acids are :

– Acid reactions

– Esterification

Acid reactions

- A carboxylic acid is a weak acid. When dissolved in water, it dissociates to produce H⁺ ions.

^- Eg. CH₃COOH <--> CH₃COO^- + H⁺

Reactions of carboxylic acids

• Carboxylic acids react with bases to form salt and water only.

• Carboxylic acids react with carbonate to produce carbon dioxide gas.

Reaction of acid - Esterification

• In the presence of a catalyst concentrated sulfuric acid, carboxylic acids react with alcohols to form a sweet-smelling compound, called an ester.

• Eg. Ethanoic acid + ethanol --> ethyl ethanoate + water

•

Esters

• The functional group of an ester is –COO- (there is a C=O bond and a C-O bond; refer to textbook on how the ester functional group looks like)

Esters are produced when an organic acid reacts with an alcohol, with a catalyst that is concentrated sulfuric acid.

Organic acid + alcohol --> ester + water

Esters

• Esters are neutral compound with a sweet smell.

• Esters are present in fruits.

• Uses of esters

– Artificial flavouring

– Solvents for organic compounds

– Vegetable oils

Macromolecules

• Macromolecules are very large molecules built up from joining together thousands of small units.

• The process of joining together thousands of small units is called polymerisation.

• The small units are called monomers.

• The large molecule formed is called a polymer.

• There are 2 groups of macromolecules:

• - synthetic polymers

• - natural macromolecules

Synthetic Polymers

• These are man-made polymers made by

–Addition polymerisation

–Condensation polymerisation

• Polymers made from addition polymerisation are called addition polymers.

• Polymers made from condensation polymerisation are called condensation polymers.

Addition Polymers

• Addition polymers are made from unsaturated monomers.

• The monomers are linked ( or added ) together to form a large molecule without the loss of any atoms. The monomers are joined together by an ADDITION reaction.

• Plastics are addition polymers formed using alkene molecules as monomers.

• Poly(ethene) is made from ethene monomers.

Condensation Polymers

• Condensation polymers are made from monomers containing alcohol, carboxylic acid or amino (-NH₂) functional groups.

• The monomers are linked together to form a large molecule with the ELIMINATION of small molecules like water. The monomers are joined together by a condensation reaction.

Examples of condensation polymers

• Two examples of condensation polymers are

– Nylon

– Terylene

Formation of nylon

• The monomers used are carboxylic acids and amines

• The monomers are joined together by amide linkages to form a polyamide. A molecule of water is eliminated.

Formation of Terylene

• The monomers used are carboxylic acids and alcohols.

• The monomers are joined together by ester linkages to form a polyester. A molecule of water is also eliminated. Terylene and nylon are examples of condensation polymers.

Uses of nylon and terylene

• Nylon and terylene are made into synthetic fibres.

• Nylon fibres are used to make ropes, fishing lines, strings for rackets and cloth for making raincoats, tents and parachutes.

• Terylene fibres are used to make clothings.

Pollution caused by plastics

• Plastics are non-biodegradable and cannot be decomposed by bacteria in the environment.

• Plastic objects accumulate and pollute the environment.

• Plastics are carbon-based polymers which burn easily to release toxic fumes.

Natural Polymers

• Natural polymers are important substances found in all plants, animals and food.

• Food is made up of 3 types of polymers:

– Proteins needed for growth

– Carbohydrate which provide the body with energy

– Fats which also provide the body with energy.