Alcohols. Flashcards
Alcohols functional group.
-OH, the hydroxyl group.
How to name alcohols.
Identify longest carbon chain, this is the stem.
Identify how many -OH functional groups e.g. 2 for -diol.
Identify where the -OH groups are on the chain(which number carbon).
Add any side chains/prefixes.
PRACTICE QUESTIONS.
Explanation of the polarity of alcohols.
Have polar O-H bonds
Because of difference in electronegativity between O and H.
Molecules are polar
IMFs are very weak London forces
Strong H bonds between polar O-H groups.
Volatility and boiling points of alcohols vs alkanes.
Intermolecular H bonds hold alcohol molecules together(liquid state)
Must break bonds to turn into a gas.
Requires more energy than overcoming weaker London forces in alkanes
Alcohols have a lower volatility than alkanes w/ the same number of C atoms.
As chain length increases, -OH group contribution decreases and resembles alkanes bp more closely.
Alcohols solubility.
Can form H bonds w/ water= more soluble
H bonds form between polar -OH group and water molecules
Soluble in water.
As chain increases in size, influence of -OH group decreases therefore solubility decreases as more closely resembles hydrocarbons.
Primary alcohols.
-OH group is attached to a carbon atom that is attached to 2 hydrogen atoms and 1 alkyl group(CH3 structure).
Methanol is the exception to this rule.
Secondary alcohols.
-OH group attached to a carbon atom that is attached to 1 hydrogen atom and 2 alkyl groups.
Tertiary alcohols.
-OH group is attached to a carbon atom that is attached to no hydrogen atoms and 3 alkyl groups.
Combustion of alcohols.
Burn completely in plentiful O2 supply
Produce CO2 and water
Exothermic reaction
More carbon atoms in alcohol chain=quantity of heat released per mole increases.
General oxidation of alcohols.
Oxidising agent=K2Cr2O7 and H2SO4
If oxidised, orange solution reduced to green solution w/ chromium ions.
Preparation of aldehydes.
Gentle heat of primary alcohol+distillation(distill aldehyde out of reaction mixture as it forms).
Prevents further reaction.
Preparation of carboxylic acids.
Heat primary alcohol strongly under reflux w/ excess potassium dichromate(VI)
Ensures all alcohol is oxidised and any aldehyde initially formed does too.
Oxidation of secondary alcohols.
Heat under reflux w/ oxidising mixture
Orange to green
Forms a ketone.
Oxidation of tertiary alcohols.
Cannot undergo oxidation reactions
Remains orange.
Not attached to a Hydrogen atom.
Dehydration of alcohols.
Water is removed from the starting material
Heat alcohol under reflux
In presence of acid catalyst(H2SO4)
Forms/product of reaction=alkenes.
Elimination reaction.
