chapter 14: alcohols Flashcards
what is the functional group of the alcohols?
-OH
hydroxyl
how do you name alcohols?
add the suffix -ol
what is the simplest alcohol?
methanol
CH3OH
what are the properties of alcohols compared to alkanes with the same number of C atoms?
less volatile
higher melting points
greater water solubility
how can you explain the polarity in alcohols?
they have a polar O-H bond due to the difference in electronegativity.
they have weak London forces.
strong hydrogen bonds between polar O-H groups.
how can you explain the low volatility and boiling points in alcohols compared to alkanes with the same number of C atoms?
in the liquid state, hydrogen bonds hold the alcohol together, they must be broken to turn it into a gas.
this requires more energy than overcoming the weak London forces in alkanes.
how can you explain the solubility of alcohols?
a compound that can form H bonds is more water-soluble.
alcohols are soluble in water because H bonds can form between the polar O-H group and the water molecules.
what happens to solubility as the chain length increases in alcohols?
decreases.
influence of the OH group decreases.
how do you classify alcohols?
primary, secondary or tertiary.
what are primary alcohols?
-OH group is attached to a carbon atom which is attached to 2 H atoms and one alkyl group (CH3).
what is a secondary alcohol?
-OH group is attached to a carbon atom which is attached to one H atom and 2 alkyl groups.
what is a tertiary alcohol?
-OH group is attached to a carbon atom which is attached to 3 alkyl groups and no H atoms.
what do alcohols produce in combustion?
carbon dioxide and water.
what type of reaction is the combustion of alcohols?
exothermic.
as the number of C atoms in the chain increases, the quantity of heat released per mole increases.
how can primary and secondary alcohols be oxidised?
with an oxidising agent:
potassium dichromate acidified with dilute sulfuric acid.
what is the colour change if the alcohol is oxidised?
orange to green
what can primary alcohols be oxidised to?
aldehydes or carboxylic acids.
how can primary alcohols produce aldehydes?
gently heated with acidified potassium dichromate.
aldehyde is distilled out as it forms, which prevents further reactions or formation of a carboxylic acid.
how can primary alcohols produce carboxylic acids?
heated strongly under reflux with an excess of acidified potassium dichromate.
reflux ensures the aldehyde oxidises to a carboxylic acid.
what are secondary alcohols oxidised to form?
ketones.
how do secondary alcohols produce ketones?
heated under reflux with oxidising mixture (K2Cr2O7).
what is a dehydration reaction?
water molecule removed from the starting material.
what does dehydration of an alcohol produce?
alkene
how do alcohols produce alkenes?
dehydration.
heated under reflux in the presence of an acid catalyst
(H3PO4 or (H2SO4).
what type of reaction is dehydration?
elimination
what do alcohols produce when they react with hydrogen halides?
haloalkanes
what type of reaction forms haloalkanes from alcohols?
substitution
how are haloalkanes produced from alcohols?
substitution reactions.
heated under reflux with sulfuric acid and a sodium halide to form HBr.
HBr reacts with the alcohol to form the haloalkane and a water molecule.
