Organic Chemistry: Alcohols PDF

# ALCOHOLS ## PREVIOUS KNOWLEDGE: - Alcohols form a homologous series that - are saturated, containing only single covalent bonds - have the general formula CnH2n+1OH - have gradation in physical properties - have similar chemical properties ## Classifying Alcohols: - Alcohols can...

# ALCOHOLS ## PREVIOUS KNOWLEDGE: - Alcohols form a homologous series that - are saturated, containing only single covalent bonds - have the general formula CnH2n+1OH - have gradation in physical properties - have similar chemical properties ## Classifying Alcohols: - Alcohols can be classified as: - Primary - Secondary - Tertiary ### Primary - has the alcohol group attached to a carbon atom with two alkyl chains and one hydrogen atom. - Example: propan-1-ol ### Secondary - has the alcohol group attached to an end of a chain. - Example: propan-2-ol ### Tertiary - has the alcohol group attached to a carbon atom with three alkyl chains attached. - Example: 2-methyl propan-2-ol - Volatility increases as the boiling point decreases. Alcohols have hydrogen bonds and this makes them less volatile than a corresponding alkane. - The alcohol functional group is polar. Methanol, Ethanol and propanol are soluble in water as their molecules form hydrogen bonds with the molecules. As alkyl chain length increases, solubility of the alcohol decreases because the aliphatic chain cannot form hydrogen bonds and this becomes the larger part of the molecule. ## ALCOHOLS - The boiling points of alcohols increase as the chain length increases. This is because as the molecules get longer, the higher the surface area of contact so stronger induced dipole - dipole intermolecular forces. This results in more energy needed to overcome these attractive forces, and therefore a higher boiling point. - The boiling points of alcohols are higher than the corresponding alkanes. This is because there are hydrogen bonds between the alcohol molecules. ## Oxidation of alcohols: ### Combustion - Alcohol can be used as fuels by undergoing combustion to transfer their stored chemical energy in a useable form such as thermal energy. - When an alcohol is completely burnt the products are carbon dioxide and water. - Example: C2H5OH(l) + 3O2 --> 2CO2 + 3H2O ### Oxidation of alcohols: - Primary and secondary alcohols can be oxidised easily; tertiary alcohols cannot. They are very resistant to oxidation and are not oxidised by common oxidising agents like acidified potassium dichromate (VI) | Class of alcohol | Reacting conditions | Product | Observation | |---|---|---|---| | Primary | gentle heating | aldehyde | colour change from orange to green | | Primary | stronger heating under reflux excess potassium dichromate (vi) | carboxylic acid | colour change from orange to green | | Secondary | heat under reflux | ketone | colour change from orange to green | | Tertiary | no reaction | | remains orange |