WM - Alcohols Flashcards
what is the functional group of an alcohol?
-OH
why do alcohols have much higher bps compared to alkanes despite having fewer C atoms?
alcohols can form strong hydrogen bonds between O and neighbouring H atom
these bonds require more energy to break
however these are not as strong as covalent bonding
how do alcohols and alkanes compare in volatility if they have the same number of C atoms?
alcohol will be less volatile
- due to hydrogen bonds between the molecules whereas alkanes have weaker van der Waals interactions
why are alcohols soluble in water?
because hydrogen bonds form with the OH bond with water molecule
as hydrocarbon chain increases what happens to the solubility of alcohols?
solubility decreases as the influence of the OH group decreases so solubility shifts to that of alkanes
primary alcohol:
OH group is attached to one carbon atom that is bonded to one other C atom
secondary alcohol:
OH group is bonded to a carbon atom thats bonded to 2 other C atoms
tertiary alcohol:
OH group is bonded to a carbon atom thats bonded to 3 other C atoms
what does combustion of an alcohol produce?
CO2 + H2O
what is needed to oxidise an alcohol?
acidified potassium dichromate
K2Cr2O7
(APD is reduced from orange to green)
what are the 2 types of chromium in oxidation reactions?
dichromate(VI) ions are orange
Chromium(III) ion are green
what products are formed from the oxidation of a 1* alcohol?
carboxylic acid or aldehyde
(final colour of reaction is green)
how are aldehydes produced form a 1* alcohol?
gently heat alcohol with K2Cr2O7
what measures are taken to insure no COOH is produced?
aldehyde is distilled out of mixture to prevent any further reaction
how are COOH produced form a 1* alcohol?
HUR with excess K2Cr2O7
why is HUR necessary to form COOH?
to ensure that the aldehyde initially formed also undergoes oxidation to COOH
what product is formed from oxidation of 2* alcohol?
ketone
(final colour of reaction is green)
how are ketones produced form a 2* alcohol?
HUR with K2Cr2O7
what product is formed from the oxidation of 3* alcohols?
nothing as they cannot be oxidised
(final colour of reaction is orange - no change)
what is HUR?
reflux is a safe method for heating volatile and flammable liquids - liquid is boiled with a vertically mounted condenser so the vapours produced can condense back into the reaction mixture
what is dehydration?
water molecules are removed
it is an example of an elimination reaction
what conditions are required for dehydration of alcohol to alkane?
alcohol is heated under reflux in the presence of conc.H2SO4 or Al2O3
what are the end products of a dehydration reaction?
alkene and water
what forms when alcohols react with hydrogen halides?
haloalkane and water
(nucleophilic substitution)
what are the conditions of a halogen substitution reaction of an alcohol?
alcohol is heated under reflux with sulfuric acid and a sodium halide - the hydrogen halide is formed in situ
