alcohols Flashcards
Describe the polarity of alcohols
Alcohols have a polar O-H bond because of the difference in electronegativity of the oxygen and hydrogen atoms, therefore they are polar
Explain, in terms of hydrogen bonding, the water solubility and volatility of alcohols compared to alkanes
Alcohols have hydrogen bonds as well as London forces, whereas alkanes only have London forces. Hydrogen bonds are stronger and so require more energy to overcome, so alcohols have a lower volatility (higher b.p) than alkanes. Alcohols can also form hydrogen bonds with water, as they are both polar, meaning alcohols are much more water soluble than alkanes.
what happens to alcohol water solubility as chain length increases?
solubility decreases as the effect of the OH group becomes relatively smaller compared to the molecule size
How are alcohols classified?
Primary, secondary and tertiary alcohols. classification is dependent on the number of H atoms and alkyl groups the carbon with the OH is attached to (e.g. primary alocohol = 1 alkyl and 2 hydrogens)
Dehydration (elimination) reaction of alcohols
Alcohol heated under reflux (+ c.H2SO4 catalyst) ———> alcohol + water
Combustion of alcohols
alcohol + oxygen (plentiful supply) ———> carbon dioxide + water
Oxidation of primary alcohols
primary alcohol + [O] ———> aldehyde + H2O (distillation)
primary alcohol + 2[O] ———> carboxylic acid + H2O (reflux)
Oxidation of secondary alcohols
Secondary alcohol + [o] → ketone + H2O (reflux)
Oxidation of tertiary alcohols
no reaction!
what solution is used to oxidise alcohols?
acidified potassium dichromate (K2Cr2O7/H2SO4)
Nucleophilic substitution of alcohols
alcohol + hydrogen halide ———> haloalkane + H2O
heated under reflux with H2SO4 + sodium halide (hydrogen halide formed in situ)
