Carbonyl Chemistry and Reactivity (5D) - Chem & Physics

Which is more electrophilic toward nucleophilic addition: an aldehyde or a ketone?

Aldehyde. Aldehydes have less steric hindrance and fewer electron-donating alkyl groups, making their carbonyl carbon more electrophilic.
What is the product class when an ester is treated with $\text{OH}^-$ and then acid workup?

Carboxylic acid + alcohol. Base hydrolysis cleaves the ester to carboxylate and alcohol, with acid workup protonating the carboxylate to the acid.
What is the product class when an ester undergoes base-promoted hydrolysis without acid workup?

Carboxylate + alcohol (saponification). Irreversible base hydrolysis cleaves the ester, yielding the carboxylate salt and alcohol without protonation.
What is the product when an acyl chloride reacts with an alcohol (with base present to neutralize HCl)?

Ester. Alcohols act as nucleophiles to attack the acyl chloride, forming the ester after chloride elimination, with base neutralizing HCl.
What is the name of the acid-catalyzed reaction that converts a carboxylic acid and alcohol into an ester?

Fischer esterification. This reversible reaction uses acid catalysis to form the ester and water, shifting equilibrium toward products with excess reactants.
What functional group is formed when a primary alcohol reacts with a carboxylic acid under acid catalysis?

Ester. Acid catalysis protonates the carboxylic acid carbonyl, enabling nucleophilic attack by the alcohol followed by water elimination.
What is the major product class when an aldehyde reacts with $\text{HCN}$ (or $\text{CN}^-$ then acid)?

Cyanohydrin. Cyanide acts as a nucleophile adding to the carbonyl, forming a new C-C bond and a hydroxyl group after protonation.
What is the product type when a ketone is treated with common oxidants such as PCC?

No reaction (ketones resist oxidation under mild conditions). Ketones lack an alpha hydrogen attached to the carbonyl like aldehydes, resisting oxidation without carbon-carbon bond cleavage.
Which carbonyl derivative is formed when a carboxylic acid reacts with $\text{SOCl}_2$ ?

Acyl chloride. Thionyl chloride converts the carboxylic acid to a highly reactive derivative by replacing OH with Cl, releasing SO2 and HCl.
Which option lists carbonyl derivatives in order of decreasing electrophilicity: acyl chloride, anhydride, ester, amide?

Acyl chloride > anhydride > ester > amide. Electrophilicity decreases due to poorer leaving groups and increased resonance stabilization from the heteroatom lone pair to the carbonyl.
What is the key resonance reason that amides are less reactive than esters toward nucleophilic acyl substitution?

Strong $n_N \rightarrow \pi^*_{C=O}$ donation reduces electrophilicity. This resonance delocalizes electrons, making the carbonyl carbon less electrophilic and less reactive to nucleophiles compared to esters.
What is the product when a carbonyl compound reacts with a primary amine under acid catalysis?

Imine (Schiff base). Acid catalysis facilitates nucleophilic addition followed by dehydration to form the C=N bond in the imine.
What is the product when a carbonyl compound reacts with an alcohol under acid catalysis and excess alcohol?

Acetal (via hemiacetal intermediate). Acid protonates the carbonyl, enabling alcohol addition to hemiacetal, followed by further substitution to the acetal with excess alcohol.
What carbonyl derivative is produced when an acyl chloride reacts with $\text{NH}_3$ or an amine?

Amide. The highly electrophilic acyl chloride undergoes nucleophilic acyl substitution with ammonia or amines, displacing chloride.
Which condition favors Fischer esterification products: excess alcohol or excess water?

Excess alcohol. Le Chatelier's principle shifts the equilibrium toward ester formation by increasing reactant concentration and removing water.
What is the key structural difference between aldehydes and ketones at the carbonyl carbon?

Aldehyde has $\text{H}$ ; ketone has two carbon substituents. Aldehydes have a hydrogen attached to the carbonyl, while ketones have two alkyl or aryl groups, affecting reactivity and naming.
Identify the carbon adjacent to a carbonyl group that can be deprotonated to form an enolate.

The $\alpha$ -carbon. The alpha-carbon bears acidic hydrogens stabilized by resonance with the carbonyl in the enolate form.
What is the product when a carbonyl compound reacts with a secondary amine under acid catalysis?

Enamine. Secondary amines form a carbinolamine intermediate that dehydrates to an enamine via alpha-hydrogen abstraction under acid conditions.
What is the product type when a carbonyl (aldehyde/ketone) reacts with $\text{NaBH}_4$ ?

Alcohol (aldehyde $\rightarrow$ $1^\circ$ , ketone $\rightarrow$ $2^\circ$ ). NaBH4 selectively reduces the carbonyl to an alcohol via hydride addition, yielding primary from aldehydes and secondary from ketones.
What is the general mechanism name for replacing a carbonyl derivative leaving group with a nucleophile?

Nucleophilic acyl substitution (addition–elimination). The mechanism involves nucleophilic addition to form a tetrahedral intermediate, followed by elimination of the leaving group to reform the carbonyl.
Which is more acidic: an $\alpha$ -hydrogen next to a carbonyl or a typical alkane hydrogen?

$\alpha$ -hydrogen next to a carbonyl. The alpha-hydrogen is acidified by resonance stabilization of the enolate anion, with pKa around 20 versus 50 for alkanes.
Identify the required intermediate formed during nucleophilic acyl substitution at a carbonyl carbon.

Tetrahedral alkoxide intermediate. Nucleophilic attack on the carbonyl carbon collapses the pi bond, forming a tetrahedral structure before leaving group departure.
What is the product when an anhydride reacts with an alcohol under nucleophilic acyl substitution?

Ester + carboxylic acid. Alcohol attacks one carbonyl of the anhydride, leading to ester formation and release of the carboxylic acid as the leaving group.
Which option correctly states the relative leaving-group ability in acyl substitution: $\text{Cl}^-$ , $\text{RO}^-$ , $\text{NH}_2^-$ ?

$\text{Cl}^- > \text{RO}^- > \text{NH}_2^-$ . Leaving group ability correlates with conjugate acid strength: HCl (strong) > ROH (weak) > NH3 (very weak), enabling easier departure.

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