MCAT Chemical and Physical Foundations of Biological Systems Flashcards: 5d Carbonyl Chemistry Reactivity

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This deck focuses on 5d Carbonyl Chemistry Reactivity, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Chemical and Physical Foundations of Biological Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which carbonyl derivative is formed when a carboxylic acid reacts with $\text{SOCl}_2$?

Answer: Acyl chloride. Thionyl chloride converts the carboxylic acid to a highly reactive derivative by replacing OH with Cl, releasing SO2 and HCl.

Flashcard 2: What carbonyl derivative is produced when an acyl chloride reacts with $\text{NH}_3$ or an amine?

Answer: Amide. The highly electrophilic acyl chloride undergoes nucleophilic acyl substitution with ammonia or amines, displacing chloride.

Flashcard 3: What is the product when an acyl chloride reacts with an alcohol (with base present to neutralize HCl)?

Answer: Ester. Alcohols act as nucleophiles to attack the acyl chloride, forming the ester after chloride elimination, with base neutralizing HCl.

Flashcard 4: What is the product when an anhydride reacts with an alcohol under nucleophilic acyl substitution?

Answer: Ester + carboxylic acid. Alcohol attacks one carbonyl of the anhydride, leading to ester formation and release of the carboxylic acid as the leaving group.

Flashcard 5: Which option correctly states the relative leaving-group ability in acyl substitution: $\text{Cl}^-$, $\text{RO}^-$, $\text{NH}_2^-$?

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

Flashcard 6: What is the key structural difference between aldehydes and ketones at the carbonyl carbon?

Answer: 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.

Flashcard 7: Which is more electrophilic toward nucleophilic addition: an aldehyde or a ketone?

Answer: Aldehyde. Aldehydes have less steric hindrance and fewer electron-donating alkyl groups, making their carbonyl carbon more electrophilic.

Flashcard 8: What is the product type when a carbonyl (aldehyde/ketone) reacts with $\text{NaBH}_4$?

Answer: 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.

Flashcard 9: What is the product type when a ketone is treated with common oxidants such as PCC?

Answer: 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.

Flashcard 10: What is the product when a carbonyl compound reacts with a primary amine under acid catalysis?

Answer: Imine (Schiff base). Acid catalysis facilitates nucleophilic addition followed by dehydration to form the C=N bond in the imine.

Flashcard 11: What is the product when a carbonyl compound reacts with a secondary amine under acid catalysis?

Answer: Enamine. Secondary amines form a carbinolamine intermediate that dehydrates to an enamine via alpha-hydrogen abstraction under acid conditions.

Flashcard 12: What is the product when a carbonyl compound reacts with an alcohol under acid catalysis and excess alcohol?

Answer: Acetal (via hemiacetal intermediate). Acid protonates the carbonyl, enabling alcohol addition to hemiacetal, followed by further substitution to the acetal with excess alcohol.

Flashcard 13: Identify the carbon adjacent to a carbonyl group that can be deprotonated to form an enolate.

Answer: The $\alpha$-carbon. The alpha-carbon bears acidic hydrogens stabilized by resonance with the carbonyl in the enolate form.

Flashcard 14: Which is more acidic: an $\alpha$-hydrogen next to a carbonyl or a typical alkane hydrogen?

Answer: $\alpha$-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.

Flashcard 15: What is the major product class when an aldehyde reacts with $\text{HCN}$ (or $\text{CN}^-$ then acid)?

Answer: Cyanohydrin. Cyanide acts as a nucleophile adding to the carbonyl, forming a new C-C bond and a hydroxyl group after protonation.

Flashcard 16: Which option lists carbonyl derivatives in order of decreasing electrophilicity: acyl chloride, anhydride, ester, amide?

Answer: Acyl chloride > anhydride > ester > amide. Electrophilicity decreases due to poorer leaving groups and increased resonance stabilization from the heteroatom lone pair to the carbonyl.

Flashcard 17: What is the key resonance reason that amides are less reactive than esters toward nucleophilic acyl substitution?

Answer: 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.

Flashcard 18: What is the general mechanism name for replacing a carbonyl derivative leaving group with a nucleophile?

Answer: 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.

Flashcard 19: Identify the required intermediate formed during nucleophilic acyl substitution at a carbonyl carbon.

Answer: Tetrahedral alkoxide intermediate. Nucleophilic attack on the carbonyl carbon collapses the pi bond, forming a tetrahedral structure before leaving group departure.

Flashcard 20: What functional group is formed when a primary alcohol reacts with a carboxylic acid under acid catalysis?

Answer: Ester. Acid catalysis protonates the carboxylic acid carbonyl, enabling nucleophilic attack by the alcohol followed by water elimination.

Flashcard 21: What is the product class when an ester undergoes base-promoted hydrolysis without acid workup?

Answer: Carboxylate + alcohol (saponification). Irreversible base hydrolysis cleaves the ester, yielding the carboxylate salt and alcohol without protonation.

Flashcard 22: What is the name of the acid-catalyzed reaction that converts a carboxylic acid and alcohol into an ester?

Answer: Fischer esterification. This reversible reaction uses acid catalysis to form the ester and water, shifting equilibrium toward products with excess reactants.

Flashcard 23: Which condition favors Fischer esterification products: excess alcohol or excess water?

Answer: Excess alcohol. Le Chatelier's principle shifts the equilibrium toward ester formation by increasing reactant concentration and removing water.

Flashcard 24: What is the product class when an ester is treated with $\text{OH}^-$ and then acid workup?

Answer: Carboxylic acid + alcohol. Base hydrolysis cleaves the ester to carboxylate and alcohol, with acid workup protonating the carboxylate to the acid.