Carbonyls (aldehydes and ketones) Flashcards
Aldehyde naming
C=O on first carbon, no number required.
Ketone naming
Counting longest carbon chaining, smallest number possible for carbonyl carbon.
What does Fehling’s and Tollens’ test for
Aldehyde
What does 2,4-DNPH test for
Carbonyl
What does iodoform test for
Methyl ketone (including ethanal), secondary methyl alcohol (including ethanol)
Intermolecular forces of aldehydes and ketones
They have London forces, permanent dipole forces. Can form H bonds but not with itself due to no H bonded to NOF therefore soluble in water.
How does Fehling’s test work
Blue solution containing CuO when warmed with aldehyde will oxidise the aldehyde and reduce the Cu2+ to Cu+ which appears as a brick red precipitate.
How does Tollens’ test work
Silver nitrate reacts with NaOH to precipitate silver oxide. This is then dissolved in ammonium hydroxide to form Ag(NH3)2 +. Silver is reduced and the aldehyde is oxidised.
How are they reduced
BH4- or AlH4- can supply hydride ions. Acts as a nucleophile and attacks the delta positive carbon.
Lithium aluminium hydride conditions
Reacts with water so dry inert solution (ether). Can happen at room temp since strong reducing agent. Must be hydrolysed with dilute acid to release alcohol from ion.
Sodium borohydride conditions
Can happen in aqueous solution or methanol, needs warming, hydrolysed with dilute acid.
Iodoform positive test
Yellow solid with antiseptic smell
Iodoform reaction products
CHI3 and RCOO-
Formula of grignard
RMgX, X = halogen and R = alkyl group
What does a grignard act like?
R- nucleophile that acts electron deficient centres
Formation of grignard
Haloalkane to granulated magnesium in ethersolvent. Set up reflux and warm with water bath.
Grignard + aldehyde
R-MgBr + CH3CHO -> R–CH(CH3)OMgBr
R–CH(CH3)OMgBr + H2O -> R–CH(CH3)OH + Mg(OH)Br
Addition of HCN to carbonyl
Can attack from above or below the trigonal plane.
Nucleophile attacks d+ carbon and heterolytic fission of pi bond with oxygen. Oxygen then negatively charged and is protonated
Hydrolysis of nitriles
Converted to carboxylic acid when heated under reflux.
In acidic conditions, gives carboxylic acid and NH4+
In alkali conditions, gives carboxylate and NH3.
Reaction of carboxylic acid to primary alcohols
With lithium aluminium hydride in dry ether (NaHBH4 is not reactive enough).
RCOOH + 4[H] -> RCH2OH + H2O
Must treat with dilute sulfuric acid at the end.
Reaction of PCl5 with carboxylic acid
Gives acyl chloride and steamy fumes of HCl.
OH group replaced with Cl atom.
Can separate products with fractional distillation
CH3COOH + PCl5 -> Ethanoyl chloride + POCl3 + HCl
Carboxylic acid react with ethanol with acid catalyst
Addition-elimination reaction, heat under reflux, slow and reversible, conc. sulfuric acid
Ethanoic acid takes proton from acid catalyst onto lone pair of O, positive charge then is delocalised and goes onto C.
Ethanol oxygen lone pair attacks C+.
Proton transfers within the molecule and molecule of water lost.
Hydrogen removed from oxygen to regenerate catalyst
Acyl chloride with water
Makes carboxylic acid vigorous at room temp. HCl steamy fumes given off
1) Nucleophilic addition of water.
2) Elimination of Cl-
3) Deprotonation
Acyl chloride with alcohol
Makes ester Cold reflux reaction. HCl steamy fumes
1) Addition of alcohol
2) Elimination of Cl-
3) Deprotonation
Concentrated ammonia with acyl chloride
Ammonium chloride and amide formed. Cold reflux.
1) Nucleo addition: d+ carbon attacked by NH3.
2) Nucleo elim: C=O forms again and Cl- leaves.
3) Deprotonation by Cl- or NH3 to form NH4.
HCl reacts with NH3 to form NH4 also.
Hydrolysis reaction of ester (acidic conditions)
Heat under reflux with dilute (to drive the equilibrium away from water towards products) sulfuric acid. Produce carboxylic acid and alcohol (can react together).
1) Ester takes a proton from hydroxonium to form a resonance structure. (+ve on C)
2) Water nucleophilic attack on carbon atom.
3) Proton transferred from bottom oxygen to oxygen with ethyl group
4) Ethanol lost
5) Deprotonation to carboxylic acid to regen catalyst
Hydrolysis reaction of ester (alkaline conditions)
Heat under reflux, irreversible because OH is much greater nucleophile then alcohol of ester.
1) Nucleophilic addition OH attacks C.
2) Nucleophilic elimination of alkoxide
3) Deprotonation
Why can’t lithal reduce alkene
Alkene has high e density on double bond, cannot be attacked, will not undergo nucleophilic addition
Grignard reagent with CO2
Dry CO2 bubbled through grignard reagent in ether then dilute acid added that adds 1 carbon and makes carboxylic acid
Grignard reagent with H2O
Produce alkane
Iodoform reaction conditions
I2 and NaOH
