MCAT Organic Chemistry - Aldehydes and Ketones I: Electrophilicity and Oxidation— Reduction

whoever rated this one star: really?

carbonyl group

a double bond between a carbon and an oxygen; strong dipole moment; no hydrogen bonding; electrophilic carbon

ketone

has two alkyl groups bonded to the carbonyl; never a terminal group

• IUPAC: alkane - -e + -one

• common names: alphabetical alkyl gorups + ketone; acetone, ethylmethylketone

• substituents: oxo-/keto-

• ring: -carbaldehyde

aldehyde

has one alkyl group and one hydrogen; always a terminal group

• IUPAC: alkane - -e + -al

• common names: formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde

• substituents: oxo-

• ring: -carbaldehyde

pyridinium chlorochromate (PCC; C5H5NH[CrO3Cl])

weak oxidant; turns terminal/primary alcohol to aldehyde

Nucleophilic addition reaction

The nucleophile attacks the carbonyl carbon, opening the carbonyl. The carbonyl cannot reform because there is no good leaving group; thus, the O– is protonated to generate an alcohol

Hydration of carbonyls

In the presence of water, aldehydes and ketones react to form geminal diols 1,1-diols)

hemiacetal/hemiketal

when aldehydes and ketones are treated by one equivalent of alcohol

acetal/ketal

when aldehydes and ketones are treated by one equivalent of alcohol

imine

a compound with a nitrogen atom double-bonded to a carbon atom; Ammonia is added to the carbonyl, resulting in the elimination of water and generation of an imine

nucleophilic substitution (SN1/SN2)

leaving group is replaced by nucleophile

common ammonia derivatives that react with aldehydes and ketones

hydroxylamine (H2N−OH) → oximes

hydrazine (H2N−NH2) → hydrazones

semicarbazide (H2N−NH−C(O)NH2) → semicarbazones

enamines

Imines and related compounds can undergo tautomerization to contain both a double bond and a nitrogen-containing group

cyanohydrins

hydrogen cyanide (HCN; pKa 9.2) with aldehydes and ketones

Oxidation of Aldehydes

form carboxylic acids

oxidzing agents: potassium permanganate (KMnO4), chromium trioxide (CrO3), silver(I) oxide (Ag2O), and hydrogen peroxide (H2O2)

Reduction by Hydride Reagents

lithium aluminum hydride (LiAlH4) and sodium borohydride (NaBH4)