⚗️ Aldehydes & Ketones
Tollens = aldehyde only (silver mirror), Fehling = aldehyde only (red ppt)
Tollens vs Fehling Test
Both tests distinguish aldehydes from ketones. Tollens' reagent (Ag(NH3)2⁺): aldehyde → silver mirror. Fehling's solution (Cu²⁺): aldehyde → brick red Cu2O precipitate. Ketones — no reaction with either.
⚗️ Aldehydes & Ketones
NaBH4 reduces both, LiAlH4 reduces both + more
Reduction of Carbonyls
NaBH4 (mild): reduces aldehydes and ketones → alcohols. LiAlH4 (strong): reduces aldehydes, ketones, carboxylic acids, esters, amides → alcohols/amines. Use NaBH4 when selectivity needed.
⚗️ Aldehydes & Ketones
Aldol = base + aldehyde/ketone with alpha-H → beta-hydroxy carbonyl
Aldol Condensation
Requires alpha-hydrogen (H adjacent to C=O). Base removes alpha-H → enolate attacks carbonyl of second molecule → aldol product. Heating causes dehydration → alpha,beta-unsaturated carbonyl.
⚗️ Aldehydes & Ketones
Grignard + aldehyde/ketone → alcohol after workup
Grignard Reaction
RMgX (Grignard) is a strong nucleophile/base. Attacks carbonyl carbon. Formaldehyde → primary alcohol. Aldehyde → secondary alcohol. Ketone → tertiary alcohol. Always do acidic workup (H3O⁺).
⚗️ Aldehydes & Ketones
Acetal = carbonyl + 2 ROH (acid catalyst, protect carbonyl)
Acetal Formation
Acetal = product of carbonyl reacting with 2 equivalents of alcohol (acid catalyst). Reaction is reversible. Acetals are stable to base and nucleophiles — used to PROTECT carbonyls during synthesis.