Aldehydes, Ketones and Nucleophilic Addition: every key term you need (+ practice quiz)
25 flashcard terms for Organic Chemistry II Topic 3, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The carbon of a carbonyl bears partial positive charge and the oxygen partial negative charge, which is why nucleophiles attack carbon and acids activate oxygen.
Aldehyde versus ketone reactivity
Aldehydes are more reactive because they have less steric bulk and less electron donation to the carbonyl carbon than ketones.
Nucleophilic addition
The defining reaction of aldehydes and ketones: the pi bond breaks as a nucleophile bonds to carbon, giving a tetrahedral alkoxide that is then protonated.
Acid catalysis of addition
Protonating the carbonyl oxygen makes the carbon far more electrophilic, allowing weak nucleophiles such as alcohols and water to add.
Hydrate formation
Water adds reversibly to a carbonyl. The equilibrium favours the hydrate only for very reactive carbonyls such as formaldehyde or those with adjacent withdrawing groups.
Hemiacetal
The first product of one alcohol adding to a carbonyl, carrying both a hydroxyl and an ether oxygen on the same carbon. It is usually unstable unless formed in a ring.
Acetal
The product of a second alcohol replacing the hemiacetal hydroxyl. It is stable to base and to nucleophiles but hydrolyses in aqueous acid.
Carbonyl protecting group
A cyclic acetal installed to shield a carbonyl while another part of the molecule reacts, then removed with aqueous acid.
Imine formation
A primary amine adds to a carbonyl and loses water. The rate peaks at mildly acidic pH, where enough carbonyl is activated without fully protonating the amine.
Enamine formation
A secondary amine gives a nitrogen-substituted alkene instead of an imine, because there is no second nitrogen hydrogen to lose.
Reductive amination
Forms an imine in the presence of a mild reducing agent that reduces it to an amine without touching the starting carbonyl.
Wittig reaction
Joins a phosphorus ylide to a carbonyl and expels a phosphorus oxide, placing a carbon-carbon double bond exactly where the carbonyl was.
Cyanohydrin
The addition product of cyanide to a carbonyl, valuable because the nitrile can later become a carboxylic acid or an amine.
Grignard reagent
A carbon nucleophile bearing magnesium that adds irreversibly to carbonyls. It is destroyed by any acidic hydrogen, so wet or protic conditions must be avoided.
Organolithium reagent
A more reactive carbon nucleophile than a Grignard reagent, able to add even to hindered or weakly electrophilic carbonyls.
Sodium borohydride
A mild hydride source that reduces aldehydes and ketones but leaves esters and acids untouched, and tolerates alcohol solvents.
Lithium aluminium hydride
A powerful hydride source that reduces nearly every carbonyl derivative, including acids, esters and amides, and reacts violently with water.
Wolff-Kishner reduction
Removes a carbonyl entirely to a methylene group through a hydrazone under strong base and heat, the basic-conditions counterpart to a thiol-based route.
Clemmensen reduction
Reduces a carbonyl to a methylene group using zinc amalgam in strong acid, chosen when the molecule tolerates acid but not base.
Baeyer-Villiger oxidation
Inserts an oxygen next to a ketone carbonyl using a peroxy acid, with the more substituted group preferentially migrating.
Conjugate addition
Addition at the carbon two positions from the carbonyl of an unsaturated system, favoured by soft, weakly basic nucleophiles.
Direct addition to an unsaturated carbonyl
Addition at the carbonyl carbon itself, favoured by hard, strongly basic nucleophiles such as organolithium reagents under kinetic control.
Organocuprate
A softer carbon nucleophile that reliably delivers its group to the position beta to the carbonyl rather than to the carbonyl itself.
Tollens test
A silver-based oxidation that distinguishes aldehydes from ketones by depositing a mirror when an aldehyde is present.
Ring size preference in cyclization
Intramolecular addition strongly favours five- and six-membered rings, where the reacting ends meet with the least strain and entropy cost.