Carbonyls Flashcards
what is the difference between an aldehyde and a ketone
an aldehyde has just one carbon bonded to the oxygens carbon ( it is at the end of the chain)
a ketone has 2 carbons bonded to the oxygens carbon (in middle of a chain)
what allows carbonyls to do hydrogen bonding
dipole with electronegative oxygen and carbon
why cant carbonyls have a hydrogen bond to them
no hydrogens present
(they still can bond to water )
why is mp of carbonyls less than alcohols
carbonyls cannot bond with themselves unlike alcohols so less h bonding and also less electrons in molecule means weaker london forces.
how do smaller aldehydes and ketones hydrogen bond
lone pairs on oxygen
very electronegative
can form H bonds with the positive hydrogens in water
why cant larger carbonyls hydrogen bond
long hydrocarbon chains disrupt hydrogen bonding within water and the hydrocarbons cannot form H bonds themselves
why cant the larger carbonyls dissolve in water
no hydrogen bonds can form
in order to dissolve the strength of hydrogen bonds must be higher than the combined strength of all IM forces present.
reaction from aldehyde to carboxylic acid
aldehyde and potassium dichromate —–> carboxylic acid
WILL NOT WORK WITH KETONE
why can ketones be oxidised
do not have a readily available hydrogen atom
oxidation of a ketone would need a very strong oxidising agent and if this was present it would just break the ketone down anyway.
what colour does aldehyde go upon adding potassium dichromate
orange to green
ketone stays orange
what happens when aldehyde heated with tollens
oxidised to carboxylic acid
silver complex ion in the tollens is reduced to silver.
producing a silver mirror
no change in ketone
what if an aldehyde is heated with fehlings solution
aldehyde will be oxidised
fehlings has copper ions which are reduced to cu2+ from Cu+
brick red colour Cu2+
no change in ketones
aldehydes vs ketones reduction
ketones reduced to secondary alcohols, aldehydes primary.
what is reduction of a ketone an example of
nucleophilic addition
addition of HCN to carbonyl compound
nucleophilic addition mechanism
HCN has hydrogen broken off
CN attacks the carbonyls carbon atom.
breaks double bond and leaves an o- on the carbonyl
the o- bonds with a H+ ion left over from the HCN
results in hydroxynitrile being formed.
what precipitate does iodoform make wwith methyl ketones
yellow
because both the iodoform and methyl ketones contain a CH3CO- group
halogenation and hydrolysis to heat an iodoform with an alkaline solution of iodine
ethanal —> triiodoethanal —–> sodium salt + triiodomethane
1st arrow is halogenation
2nd is hydrolysis
what other compound will form a yellow precipitate in iodoform
alcohols containing a R-CH(OH)-CH3 group
