carbonyls + carboxylic acids + esters Flashcards
carbonyl definition
an organic moleucle that contains a C=O group
give 3 examples of carbonyl compounds
aldehydes, ketones, carboxylic acids
outline the test for carbonyl groups
- react sample with 2,4-DNP, a pale orange solution
POSITIVE= a condensation reaction will occur and a yellow-orange precipitate is formed
after a positive test result with 2,4-DNP, what can be done to identify the carbonyl compund
the melting point of the precipitate formed can be found, then this can be compared to a database to identify the carbonyl compound
outline a test for aldehydes
- prepare a solution of 3cm3 AgNO3(aq) + 1 drop of NaOH to produce AgO a brown precipitate
- add NH3 dropwise until precipitate redissolves- this is tollens reagent
- add tollens reagent to the sample in a water bath at around 50C-60C
POSITIVE= a silver mirror will form as the aldehyde is oxidised to a carboxylic acid as Ag+(aq) + e-»_space; Ag(s)
why will ketones not react with tollens reagent
ketones cannot be oxidised, as there is no H group on the carbon with the C=O group to lose
by what mechanism do ketones normally react
nucleophilic addition
compare the reactivity of carbonyls and alkenes
carbonyls tend to be more reactive than alkenes, as the C=O bond is polar, due to the electronegativity difference between C and O, causing electron density to lie closer to the O, creating a dipole, so nucleophiles are attracted to the slight positive charge on the C atom
whereas C=C bonds are non polar
give the reagents and conditions to go from an aldehyde/ketone to an alcohol
reagent - NaBH4
conditions - aqueous
- just write it as [H] in equations, so you don’t have to worry about side products, but don’t forget to balance!
give the reagents and conditions to go from an aldehyde/ketone to a hydroxynitrile
reagents - NaCN + H2SO4 to form HCN in situ - HCN can be used in equations
conditions - aqueous
why is HCN alone not used as a reagent
HCN is a colourless + poisonous liquid, and is also very volatile as it boils slightly above room temp, so it cannot be safely used in a lab
give the reagents and conditions to go from an aldehyde to a carboxylic acid
reagents - K2Cr2O7
conditions - H2SO4 + heat under reflux
colour change from orange to green will occur
- this reaction can also be used to identify an aldehyde
carboxylic acid definition
a compound with C=O carbonyl and OH hydroxyl functional groups bonded to the same carbon atom
why do carboxylic acids have high water solubility
C=O and O-H bonds are both polar, and these groups allow carboxylic acids to form hydrogen bonds with H2O
what structural factors affect the solubility of carboxylic acids
carbon chain length - as the length of the alkyl chain increases, solubility decreases as this is non polar
number of carboxyl groups - as number of carboxyl groups increases, solubility increases - dicarboxylic acids are very soluble