Chemical Reactions Flashcards
What type of reactions do aldehydes and ketones undergo
Nucleophilic addition reactions
Mechanism of Nucleophilic addition reactions STEP 1
Nucleophile attacks the electrophilic carbon of the polar carbonyl group.(SLOW PROCESS)
STEP 2 of mechanism
The hybridization changes from sp2 to sp3 and tetrahedral alkoxide intermediate is formed
STEP 3 of mechanism
The intermediate captures a proton to give an electrically neutral product(FAST PROCESS)
STEP 4 of mechanism
Addition of Nu- and H+ across the carbon oxygen double bond
What happens when weak nucleophiles are used?
An acid catalyst must be used for the reaction to proceed
Are aldehydes or Ketones more susceptible toward nucleophilic reactions
Aldehydes as
- sterically, the presence of 2 substituent groups hinders the approach of nucleophile in ketones whereas in aldehydes there is only 1 substituent group.
- electrically, 2 alkyl groups in ketones reduce its electrophilicity (lesser polarisation).
What happens when the reaction is slow when aldehydes and ketones react with HCN
HCN is catalysed by a base and yields a cyanide ion which is a stronger nucleophile.
Addition of HCN yields
Cyanohydrins.
How can a hydrogen sulphite addition compound be converted back to the original carbonyl compound.
Treat it with dilute mineral acid or alkali.
Addition of alcohol with aldehydes
Monohydric alcohol + Aldehydes–
->Hemiacetal + Alcohol —>Acetal
Addition of which alcohol with ketone
Ethylene glycol
Addition of ethylene glycol with ketone yields
Ethylene glycol ketals
Reagent used to reduce aldehydes and ketones to alcohols
sodium borohydride(NaBH4) and litium aluminium hydrid(LiAlH4)
Clemmensen Reduction
Carbonyl group + Zinc amalgam and HCl is reduced to CH2 group
Wolff-Kishner Reduction
Carbonyl group + NH2NH2 to form hydrazone and heat with sodium/potassium hydroxide in ethylene glycol to reduce to CH2
Oxidising agents
Nitric Acid, Potassium permanganate and potassium dichromate
How is oxidation of Ketone different from that of aldehydes
Oxidation of Ketones involves carbon-carbon bond cleavage resulting in a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.
How to distinguish aldehydes from ketone
Tollens’ test and Fehling’s Test(for aldehydes) and Haloform(Ketones)
Tollens’ reagent
Ammoniacal Silver nitrate solution
Tollens’ Test
RCHO+2[AG(NH3)2] —>silver mirror and carboxylate anion
Fehling’s solution A
aqueous copper sulphate solution
Fehling’s solution B
Rochelle salt (Sodium potassium tartarate)
Fehling’s Test
Aldehyde + Fehling’s reagent (A+B)—–
->reddish brown precipitate + carboxylate anion
Which aldehyde does not respond to fehling’s test
Aromatic aldehydes due to strong double bond character within benzene ring.
Haloform reaction
Methyl ketone + sodium hypohalite —-
->sodum salts of carboxylic acids and is converted to haloform.
What is iodoform reaction used for
Iodoform + sodium hypoiodite is used for detection of CH3CO or CH3CH(OH) which produces CH3CO on oxidation.
What is the reason behind the acidity of 𝛼-hydrogen atoms of carbonyl compounds?
Strong electron withdrawing effect and resonance stabilization of the conjugate base.
Aldol reaction
One 𝛼-hydrogen undergo a reaction in the presence of dilute alkali to form aldol or ketol.
Aldol condensation
The aldol and Ketol lose water to give 𝛼,β-unsaturated carbonyl compounds.
Cross aldol condensation
carried out between two different aldehydes/ketones
How many products are formed when both contains 𝛼-hydrogen atoms
4
Cannizzaro Reaction
yields carboxylic acid and alcohol. for aldehydes with no 𝛼-hydrogen atom. undergoes self-oxidation and reducation on heating with KOH or NaOH.
Electrophilic substitution reaction is observed in
Aromatic aldehydes and Ketones.(HNO3 AND H2SO4)
Formalin
formaldehyde- to preserve biological specimens and to prepare bakelite
Acetaldehyde
Manufacture of acetic acid, vinyl acetate, drugs and polymers.
Benzaldehyde
in perfumery and dye industries
Acetone and ethyl methyl ketone
industrial solvent
Camphor, vanillin and acetophenone
known for their odours and flavors.
