Alcohols

• An alcohol molecule is named based on the higher priority functional group. In the case of an aldehyde containing an additional -OH functional group, The prefix would be hydroxy with the suffix anal.
• In primary alcohols, the carbon atom bonded to the hydroxyl functional group is bonded to one other carbon atom. An example of a primary alcohol is ethanol.
• Methanol is also considered a primary alcohol, despite not following the rule.
• Secondary and tertiary alcohols have two and three carbon atoms bonded to the carbon attached to the hydroxyl group respectively.
• How an alcohol reacts is largely based on whether it is a primary, secondary or tertiary alcohol.
• Alcohols have a higher boiling point than their respective alkane with the same number of carbon atoms.
• Alcohols are polar molecules due to their hydroxyl group, and so have the ability to form both London forces and strong hydrogen bonds with neighbouring molecules, giving them their higher boiling point
• the volatilty of a molecule tells us how readily a molecule turns into a gas.
• Because alcohols have a higher boiling point than their respective alkanes, overall, alcohols are less volatile than alkanes.
• As the number of carbon atoms in the alkyl chain of an alcohol and an alkane increases, the boiling point of the two molecules get closer together, because the contribution of hydrogen bonding in the alcohol decreases and the contribution of London forces increases.
• alcohols contain a polar hydroxyl group with an oxygen atom, that is able to form hydrogen bonds with a water molecule, thus making alcohols miscible/soluble in water.
• As you increase the length of the carbon chain of an alcohol, its miscibility decreases. This is because more of the molecule becomes non-polar and unable to form hydrogen bonds with water.
• Oxidising a primary alcohol via distillation produces an aldehyde and water. This occurs in the presence of an oxidising agent such as K2Cr2O7, potassium dichromate.
• An oxidising agent is also often presented as [O]
• During the oxidisation of a primary alcohol, [O] is reduced from the dichromate (VI) ion, which is orange, to the chromium (III) ion, which Is green.
• Aldehydes have a relatively low boiling point as they are unable to form hydrogen bonds. Because of this we can separate alcohols from aldehydes using distillation.
• Aldehydes very easily oxidised, so if we want to only make an aldehyde, we must remove it from the reaction very quickly.
• Having excess alcohol and limited oxidising agent would favour the production of an aldehyde in oxidation.
• Oxidising an aldehyde produces a carboxylic acid. This is done by heating the reaction mixture under reflux.
• producing a carboxylic acid from an alcohol would require two molecules of an oxidising agent, so to ensure the reaction occurs we use excess oxidising agent.
• When heating under reflux, any volatile products are condensed and returned to reaction mix meaning we can heat until the reaction is complete.
• Our mixture containing our product may also contain any unredacted alcohol and aldehyde, but because carboxylic acids can form hydrogen bonds and so have a higher boiling point, we can separate them by distillation.
• When a secondary alcohol is oxidised, we make a ketone and water. Using Potassium Dichromate, the solution would turn from orange to green.
• We cannot further oxidise a ketone as there are no available hydrogen atoms to remove from the carbon atom which is bonded to the oxygen atom.
• We cannot oxidise tertiary alcohols as there are no hydrogen atoms bonded to the carbon atom, that is attached to the hydroxyl group, that we can remove.
• Ketones cannot form hydrogen bonds and so have a lower boiling point that their respective alcohols, therefore we can separate ketones from our alcohols via distillation.
• An alcohol can undergo an elimination reaction to form an alkene, in the presence of hot sulfuric acid or aluminium oxide.
• An alcohol can also undergo elimination reactions to esters by reacting with carboxylic acids in presence of a hot sulfuric acid catalyst.
• an elimination reaction involved producing a small molecule from a larger, parent molecule. Therefore dehydration is an example of an elimination reaction.
• To produce an alkene from an alcohol by dehydration, we heat under reflux in the presence of hot concentrated sulfuric acid or phosphoric (V) acid.
• Dehydration of pentan-2-ol can produce two structural isomers of pent-1-ene and pent-2-ene, however pent-2-ene has two geometric isomers. Therefore from this reaction, we could produce 3 different product.