Aldehydes and Ketones Nomenclature

• Aldehydes and ketones contain an acyl group bonded to hydrogen or another carbon

Acyl Group Configurations

• Aldehydes contain an acyl group bonded to a hydrogen atom
• Ketones contain an acyl group bonded to another carbon atom

Nomenclature

• The longest continuous carbon chain dictates the base name for aldehydes
• Replace the "-e" alkane ending with "-al" for aldehydes
• Indicate substituents as usual
• The position of the -CHO group doesn't need specification as it is C-1.
• For compounds with two aldehyde functions, add the suffix "-dial" to the alkane name.
• For ketones, replace the "-e" alkane ending with "-one
• Number the carbon chain to give the carbonyl group the lowest number

IUPAC Nomenclature

• It's acceptable to name ketones using functional class nomenclature
• Name the groups attached to the carbonyl group separately, followed by "ketone."

Common Names Acceptable

• Examples of acceptable common names for aldehydes include formaldehyde (methanal) and acetaldehyde (ethanal)
• Examples of acceptable common names for aldehydes include benzaldehyde (benzenecarbaldehyde)
• Common ketone names are acetone, acetophenone, and benzophenone
• The suffix "-phenone" indicates an acyl group attached to a benzene ring

Formyl Groups

• When a formyl group (-CH=O) links to a ring, add the suffix "-carbaldehyde" .
• Examples include cyclopentanecarbaldehyde, 2-Naphthalenecarbaldehyde

Structure and Bonding

• The carbonyl group, along with atoms directly attached, lie in the same plane
• Bond angles within aldehydes and ketones approximate 120°
• At 122 pm, the carbon-oxygen double bond distance is shorter than the carbon-oxygen single bond distance in alcohols/ethers (141 pm).
• Molecular dipole moments are substantial, showing polarity
• Carbonyl's bonding follows an sp² hybridization model

Resonance and Polarization

• The carbonyl group shows polarization, with a partially positive carbon and partially negative oxygen
• Electron delocalization is shown by major resonance structures

Stabilization via Alkyl Groups

• Alkyl substituents stabilize carbonyl groups by releasing electrons
• This is similar to stabilizing carbon-carbon double bonds and carbocations

Stability Comparison

• A ketone carbonyl group is more stable than an aldehyde carbonyl group
• A disubstituted double bond in alkenes is more stable than a monosubstituted double bond

Physical Properties

• Aldehydes and ketones have higher boiling points than alkenes due to polarity
• Dipole-dipole attractive forces contribute to this higher boiling point
• They have lower boiling points than alcohols because they can't form hydrogen bonds to each other due to no OH group directly attached to carbonyl
• Aldehydes and ketones can bond to the hydrogen of OH groups, and are more water soluble than alkenes, but less soluble than alcohols

Natural Occurrence

• Aldehydes and ketones often occur naturally
• A few examples include: undecanal, 2-heptanone, trans-2-hexenal, citral, civetone, jasmone

Synthesis Origins

• They are synthesized in labs, originating from reactions involving alkenes, alkynes, arenes, and alcohols

Aldehyde Synthesis Pathway

• Carboxylic acids are converted to aldehydes indirectly
• The acid is reduced to a primary alcohol which is then oxidized to the aldehyde

Hydration Reaction

• Aldehydes and ketones react with water, achieving rapid equilibrium
• Overall, this reaction adds water's elements to the carbonyl group
• This addition process bonds hydrogen to carbonyl oxygen and hydroxyl to carbonyl carbon

Equilibrium and Structure

• Positioning equilibrium depends on groups attached to C=O
• Both steric and electronic environments affect this
• Electronic effects control equilibrium more than steric ones

Catalyzation of Oxygen Bonding

• Basic catalysts expedite rate of nucleophilic addition.
• Hydroxide ions are more reactive as nucleophiles than ambient water molecules.
• Acid catalysts activate the carbonyl for easier weak nucleophile attacks

Cyanohydrin Formation

• Hydrogen cyanide yields both a hydroxyl and cyano group-bonded product
• Named "cyanohydrins"

Catalyzation of Cyanide Bonding

• Catalyzing needs cyanide ion, however, HCN doesn't provide enough
• Free cyanide ions in sufficient amounts are ensured by adding acid to carbonyl compound and sodium/potassium cyanide solution
• Cyanohydrin formation reverses depending on factors, but aldehydes and unhindered ketones have the best yields

Uses for Cyanohydrins

• Conversion to carboxylic acid function (CO2H) by hydrolysis
• Conversion to an amine of the type CH2NH2 by reduction

Acetal Formation

• This requires acidic conditions
• The nucleophilic addition product of the alcohol to the carbonyl group is a hemiacetal but a geminal diether known as acetal is isolated in practice
• The hemiacetal is converted to an acetal via a carbocation intermediate stabilized through releasing electrons from their substituents

Reversibility

• Acetal formation is reversible in acid and equilibrium is established between reactants i.e. carbonyl compounds, alcohol, and the acetal product.
• Favorable acetal formation arises from most aldehydes where excess alcohol is present
• Ketone equilibrium is reverse.

Diols

• Diols having two hydroxyl groups in a 1,2 or 1,3 relationship yield cyclic acetals on reaction with aldehydes or ketones. five-membered cyclic acetals are the most famous
• Equilibrium is then more favorable by removing water formed in reaction by azeotropic distillation while using benzene or toluene

Acetal Applications

• Acetals protect carbonyl groups during incompatible reactions

Imine Reaction

• Reaction with primary amines happens via two-stage reaction
• The amine adds to the carbonyl group forming a carbinolamine while carbinolamine undergoes dehydration to form the N-alkyl- or N-aryl-substituted imine.

Wittig Reaction

• Uses phosphorus ylides (Wittig reagents) to turn aldehydes and ketones to alkenes

Wittig Reaction Solvents

• Wittig reactions happen with solvents
• Tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO)

Wittig Reaction Location

• The double bond connects a carbon in the original C=O group (aldehyde or ketone) and negatively charged carbon of the ylide.

Charge Distribution

• High electrons mean carbon becomes nucleophilic against C=O in which there can be reactions.
• P-O is strong, estimated to go beyond 540 kJ/mol (130 kcal/mol)