14. Alcohols Flashcards
Where is the OH in aromatic alcohols?
attached directly to the ring
Why do alcohols have higher boiling points than alkanes?
alcohols have permanent d-d interactions and H bonds, which are the strongest kind of IMF, requires more energy to break than just LDFs in alkanes
Why would 2-methylpropan-2-ol have a lower bp than butan-1-ol?
2-mp2 is more branched, reduces contact points & LDFs, less energy required to overcome IMFs and boil
Why would butan-2-ol have a lower bp than butan-1-ol?
butan-1-ol is slightly longer and butan-2-ol cannot pack as closely due to branches of OH group, meaning LDFs slightly weaker
Are alcohols miscible with water and what is the trend with increasing Mr ?
low Mr yes bc H bonding
higher Mr less miscible bc chain is too long to fit between H2O molecules bc it is non-polar and not attracted to H2O molecules
Are alcohols a good solvent?
yes for both organic and aqueous (universal-esque solvent)
2 chemical properties of alcohols
are bases (proton acceptors) are nucleophiles (electron pair donors)
Why are longer chain alcohols worse fuels than shorter chain?
vaporise less easily: there are too many IMFs to break: inefficient to overcome all LDFs
What catalyst is used in oxidation of alcohols? What is the colour change?
acidified potasium dichromate (K2Cr2O7)
changes orange to green
actual reagent is acidified dichromate ion (H+/Cr2O7^2-) (acidified by H2SO4)
What do you get if you heat gently and distil the product of the oxidation of a primary alcohol?
aldehyde
Why can you distil off an aldehyde?
it has no H bonding so it can be distilled at the lowest boiling point before being further oxidised FINISH THIS
What are the conditions for creating carboxylic acids?
primary alcohol, heat strongly under reflux, acidified potassium dichromate
or aldehyde, keep heating, reflux, acidified potassium dichromate
What is potassium dichromate in the oxidation of alcohols?
oxidising agent
How do you make ketones when oxidising alcohols?
secondary alcohol, reflux, acidified potassium dichromate
Why can you not oxidise a tertiary alcohol?
the alcohol group is attached to a carbon that’s attached to 3 other carbons, therefore it cannot lose a hydrogen from the central carbon to become an aldehyde, carboxylic acid or ketone
Why do we use reflux?
prevents the loss of volatile substances and increases yield
In which oxidations of alcohol is water created?
alcohol => aldehyde
alcohol => carboxylic acid
alcohol => ketone
What are the important parts to include when drawing distillation apparatus?
inner tube, heat source, pear shaped flask, in (base) and out (top) flows of water
Why do you heat strongly when making a carboxylic acid?
if aldehyde is created, it condenses back into the mixture and gets oxidised again to carboxylic acid
What are the conditions for the dehydration of alcohols => alkenes + water?
reflux, conc. H3PO4 catalyst
What are the reagents and conditions for the esterification of alcohols?
alcohol + carboxylic acid (or acyl chloride)
small vol. conc. H2SO4 catalyst (homogeneous), reflux/heat
what are the uses of esters?
flavourings, solvents, plasticisers
Where does the OH of the water produced in esterification come from?
the carboxylic acid
What is the product of a substitution reaction of alcohol?
haloalkane + water
What are the reagents and conditions for the substitution reactions of alcohols?
hydrogen halide, NaBr and H2SO4
H2SO4, reflux, sodium halide
How is the hydrogen halide made in substitution reactions of alcohols?
in-situ by refluxing the alcohol with NaBr and H2SO4
KATY REMEMBER DONT DO MOLECULAR FORMULA DO STRUCTURAL
don’t fuck it up x
In what 3 ways can you prepare alcohols?
haloalkanes (nucleophilic substitution)
aldehydes (reduction)
alkenes (direct hydration: steam + phosphoric acid)
What are some uses of alcohols?
alcoholic drinks, solvent (meths), fuel, chemical feedstock
What is the bond angle around the func. group carbon of an aldehyde?
120 degrees
