4.2.1 - alcohols Flashcards
why are alcohols polar?
they have a hydroxyl group. oxygen is more electronegative than carbon, so attracts the electrons in the C-OH bond away from the carbon atom
how do the boiling points of alcohols compare to alkanes of a similar chain length?
alcohols have higher boiling points, and are less volatile.w
why do alcohols have high boiling points? (and compare to that of alkanes)
alcohols have hydrogen bonding between molecules. alkanes have induced dipole-dipole interactions between molecules. Hydrogen bonds are stronger than induced dipole-dipole interactions so require more energy to overcome, and so alcohols have higher boiling points.
why are alcohols soluble in water?
they contain -OH groups. this means they can form hydrogen bonds with the water.
more -OH groups means higher solubility.
when alcohols are dissolved in water, is the solution acidic, neutral or alkaline?
neutral
describe and explain the trend in solubility of alcohols as chain length increases
as chain length increases, solubility decreases.
there are more points of surface contact between molecules of longer chain length, so the induced dipole-dipole interactions between molecules are stronger. these break up the hydrogen bonds between molecules.
why are alcohols added to petrol mixtures?
prevent incomplete combustion.
there is an internal supply of oxygen in the form of an -OH group.
why do alcohols make good fuels?
they have high enthalpies of combustion - produce a lot of energy per mole of alcohol burnt.
what are the reagents/conditions for the synthesis if an alkene from an alcohol?
H2SO4 or H3PO4 and heat
what kind of reaction is the synthesis of an alkene from an alcojol?
elimination reaction (aka dehydration)
how are alcohols classified?
can be primary, secondary or tertiary alcohols.
what is a primary alcohol?
the -OH group is attached to a carbon that is attached to 1 other carbon (alkyl group)
what is a secondary alcohol?
the -OH group is attached to a carbon that is attached to 2 other carbons (alkyl groups)
what is a tertiary alcohol?
the -OH group is attached to a carbon that is attached to 3 other carbons (alkyl groups)
describe the partial oxidation of a primary alcohol.
reagents: K2Cr2O7 (represented at [O] in equations), H2SO4
conditions: distillation apparatus
organic product: aldehyde
also produces 1 mol of water
observations: colour change from orange to green
describe the complete oxidation of a primary alcohol
reagents: K2Cr2O7 (represented at [O] in equations), H2SO4
conditions: reflux apparatus
organic product: carboxylic acid
also produces 1 mol of water
observations: colour change from orange to green
describe the complete oxidation of an aldehyde
reagents: K2Cr2O7 (represented at [O] in equations), H2SO4
conditions: reflux apparatus
organic product: carboxylic acid
describe the oxidation of a secondary alcohol
reagents: K2Cr2O7 (represented at [O] in equations), H2SO4
conditions: distillation or reflux apparatus
organic product: ketone
also produces 1 mol of water
observations: colour change from orange to green
describe the oxidation of a tertiary alcohol
cannon be oxidised
how can you test for the presence of a primary/secondary alcohols?
add a few drops of acidified potassium dichromate and concentrated H2SO4
colour change from orange to green in the presence of primary and secondary alcohols
tertiary alcohols will not react, there will be no colour change
