ch 6 - Aldehydes and Ketones 1: Electrophilicity and Oxidation-Reduction Flashcards Preview

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double bond between a carbon and an oxygen



two alkyl groups bonded to the carbonyl; never terminal



one alkyl group bonded to carbonyl and one hydrogen; always terminal


naming aldehydes

replace -e at the end of alkane name with suffix -al; as substituent, use prefix oxo-; if attached to ring suffix -carbaldehyde is used


naming of ketones

replace -e of alkane with suffix -one. when naming common names, two alkyl groups are named alphabetically followed by -ketone. as substituents, use prefix oxo- or keto-


boiling point of ketones and aldehydes

higher than parent alkanes because dipole moments associated with polar carbonyl groups increase intermolecular attractions but less than alcohols because no hydrogen bonding is present in these


reactivity of aldehydes and ketones

double bond to oxygen causes these to be more electron-withdrawing than alcohols; act as electrophiles (targets for nucleophiles) which leaves a partial positive charge on the carbon; aldehydes are generally more reactive toward nucleophiles because of less steric hindrance and few electron-donating alkyl groups


formation of aldehyde from primary alcohol

PCC the only means by which a primary alcohol is partially oxidized to an aldehyde; with stronger oxidants, aldehydes will continue to carboxylic acids


ketone from secondary alcohol

any strong oxidant: Na2Cr2O7, K2Cr2O7, CrO3, PCC; reaction stops at the ketone stage and does not oxidize further


geminal diols

aldehydes and ketones react with water to form this (1,1 diols): nucleophilic oxygen in water attacks the electrophilic carbonyl carbon; can increase rate by adding small amount of catalytic acid or base


formation of hemiacetal or hemiketal

aldehyde/ketone reacted with one equivalent of alcohol (nucleophile in this reaction), hemiacetal or hemiketal results, respectively; marked by retention of hydroxyl group (end point in basic conditions)


formation of acetals and ketals

result from two equivalents being added to aldehydes and ketones respectively. proceeds by nucleophilic substitution reaction (SN1) and is catalyzed by anhydrous acid; these are used as protecting groups and can easily be reversed by aqueous acid and heat


formation of imine

nitrogen and nitrogen-based functional groups act as good nucleophiles because of lone pair on nitrogen; this results from ammonia reacted with aldehyde or ketone; it is a nitrogen atom double-bonded to a carbon atom; is a condensation reaction and an example of nucleophilic substitution


condensation reaction

reaction in which a small molecule is lost during the formation of a bond between two molecules (ex is formation of imines)


common ammonia derivative molecules that react with aldehydes and ketones

ammonia (NH3) and its derivatives, hydroxylamine (N2H-OH), hydrazine (H2N-NH2), semicarbazide (H2N-NH-C(O)NH2) forming oximes, hydrazones, and semicarbazones respectively



formed from tautomerization of imines and related compounds


formation of cyanohydrins

aldehydes/ketones reacted with HCN (cyanide) which has both triple bonds and an electronegative nitrogen atom; after hydrogen dissociates, nucleophilic cyanide anion can attack the carbonyl carbon atom. this is the result once the oxygen has been reprotonated; has stability from the newly formed C-C bond


oxidation of aldehydes to carboxylic acids

CH3C(double bond O)H + either one of these: KMnO4, CrO3, Ag2O, H2O2 -> CH3 C(double bond O) OH (a carboxylic acid) [note that ketones cannot be oxidized more because they are already as oxidized as a secondary carbon can get.


reduction of aldehydes and ketones to alcohols

often performed with hydride reagents: most commonly lithium aluminum hydride (LiAlH4) and sodium borohydride (NaBH4)