Alcohols Flashcards
Why does the solubility of alcohols in water decrease as chain length increases?
The –OH group is the only part that interacts with (or dissolves in) water. As the chain length increases, the effect of the –OH decreases and that of the non-polar (water insoluble) carbon chain becomes more important.
How do you tell if an alcohol is primary, secondary or tertiary?
It depends on how many carbons are bonded to the carbon that the OH is bonded onto.
What intermolecular forces can alcohols have?
Intermolecular forces:
H bonds
London forces
Permanent dipoles
What physical properties of alcohols arise from the ability to H bond?
- High melting point/boiling point for molecules of their size: Low volatility.
- Small alcohols are water soluble
What are some uses of ethanol?
- Drinking
- As a solvent - Polar and a non-polar end
- As a fuel - Ethanol burns more cleanly than other fuels as it has fewer carbons and it already has an oxygen in the molecule. It is also renewable.
How do alcohols combust?
Alcohol + O2 —> CO2 + H2O
What is the dehydration of alcohol?
The OH and an H group (from the next-door carbon) from the alcohol break away from the alcohol and react to form water. This creates an alkene.
What two chemicals are needed to produce an oxidising agent for alcohols
Sodium / Potassium dichromate solution (Na2Cr2O7 or K2Cr2O7)
Dilute sulphuric acid
What is the observation for the correct formation of the alcohol oxidising agent?
Reaction mixture turns from orange to green (or blue)
What functional groups can form from the oxidation of alcohols?
Aldehydes
Ketones
Carboxylic Acid
What conditions are required for the preparation of an aldehyde from a primary alcohol?
Acidified potassium dichromate, heat gently and distil off the product
What conditions are required to prepare a carboxylic acid from a primary alcohol?
Heating with reflux in the presence of excess acidified potassium dichromate
What conditions are required to oxidise secondary alcohols and what is formed from this?
Heat under reflux with acidified potassium dichromate. This forms ketones.
What happens when tertiary alcohols are heated with acidified potassium dichromate?
Nothing
What mechanism is used in alcohol substitutions
Nucleophilic substitution
