4.2.1 Alcohols Flashcards
(18 cards)
What are the bonding properties of alcohols?
- Have a polar O-H bond due to the difference in electronegativity
- Hydrogen bonds between O-H groups
- Weak London forces
What are the volatility properties of alcohols?
- Alcohols are less volatile than alkanes
- Hydrogens must be broken which requires more energy
What are the solubility properties of alcohols?
- Alcohols are soluble in water
- Hydrogen bonds form between the O-H group and water molecules
- As chain length increases, solubility decreases
What are primary alcohols?
OH group is attached to a C atom with 2 H atoms and 1 alkyl/R group
What are secondary alcohols?
OH group is attached to a C with 1 H atom and 2 alkyl/R groups
What are tertiary alcohols?
OH group is attached to a C with no H atoms and 3 alkyl/R groups
What is the combustion of alcohols?
- Burn completely to form CO2 and H2O
- Exothermic reaction
How is potassium dichromate an oxidising agent?
- Dichromate (VI) ions are reduced to chromium (III) ions
- Solution changes from orange to green
What is the oxidation of primary alcohols to form aldehydes?
- Gently heating a primary alcohol with acidified potassium dichromate forms an aldehyde
- Aldehyde is distilled as it forms
- Water is also formed
What is the oxidation of primary alcohols to form carboxylic acids?
- Strongly heating a primary alcohol under reflux with excess acidified potassium dichromate forms a carboxylic acid
- Excess K2Cr2O7 ensures all alcohol is oxidised
- Reflux ensure any aldehyde undergoes further oxidation
What is Tollens reagent?
- Confirms aldehydes
- [Ag(NH3)2]+ is reduced to Ag
- Results in a layer of silver forming
What is Fehling’s solution?
- Confirms aldehydes
- Cu2+ is reduced to Cu+ (in Cu2O)
- Turns from blue to brick red precipitate
What is the oxidation of a secondary alcohol to form a ketone?
- Heating a secondary alcohol under reflux with acidified potassium dichromate forms a ketoneW
What happens to tertiary alcohols when added to acidified potassium dichromate?
- Do not undergo oxidation
- Remains orange
What is the elimination of H2O in alcohols?
- Heating under reflux at 180°C with an acid catalyst
- Forms an alkene
- Catalyst is concentrated H2SO4 or H3PO4
- Dehydration
What is the mechanism for the elimination of water from alcohols?
- Acid catalyst is a source of H+
- Used to protonate the OH (curly arrow from lone pair on OH to H+)
- H2O lost to for a carbocation (curly arrow from bond to O+)
- Alkene forms (curly arrow from bond to H to where double bond will form)
What is the substitution of alcohols?
- React with hydrogen halides to form haloalkanes
- Heated under reflux with sulfuric acid and a sodium halide
- Hydrogen halide is formed in situ
What is the mechanism for nucleophilic substitution of alcohols?
- X- attacks C (curly arrow from X- to C)
- Bond breaks between C and OH (curly arrow from bond to OH)
