CHEM 2081 Exam IV - study set

reduction patterns and test prep

TERM: What does LiAlH4 reduce?

ANSWER: Everything — aldehydes

TERM: What does NaBH4 reduce?

ANSWER: Only aldehydes and ketones.

TERM: What does DIBAL (–78°C) do to esters?

ANSWER: Reduces esters to aldehydes.

TERM: What does LiAlH(OtBu)3 do to acid chlorides?

ANSWER: Reduces acid chlorides to aldehydes (selective

TERM: What does SOCl2 do to alcohols?

ANSWER: Converts alcohols to alkyl chlorides.

TERM: What does SOCl2 do to carboxylic acids?

ANSWER: Converts carboxylic acids to acid chlorides.

TERM: What does PCC oxidize a primary alcohol to?

ANSWER: An aldehyde.

TERM: What does CrO3/H2SO4 oxidize primary alcohols to?

ANSWER: Carboxylic acids.

TERM: What does CrO3/H2SO4 oxidize secondary alcohols to?

ANSWER: Ketones.

TERM: What does H2 with Lindlar catalyst do?

ANSWER: Reduces alkynes to cis alkenes.

TERM: What does excess H2 with Pd do?

ANSWER: Fully hydrogenates alkenes or alkynes into alkanes.

TERM: What happens when CH3MgBr reacts with an ester?

ANSWER: Adds twice

TERM: What does NaOEt do to esters?

ANSWER: Forms an enolate that undergoes SN2 alkylation with alkyl halides.

TERM: What does NaOH and heat do to carbonyl compounds?

ANSWER: Aldol condensation

TERM: What does H2SO4 and H2O do to alkenes?

ANSWER: Markovnikov hydration

TERM: What type of enolate does LDA at –78°C form?

ANSWER: The kinetic enolate (from the least substituted α-H).

TERM: Which hydrogen is most acidic in β-dicarbonyls?

ANSWER: The central α-hydrogen between the two carbonyls.

TERM: Which is more acidic: phenol or alcohol?

ANSWER: Phenol.

TERM: Acidic C–H order (most acidic to least acidic)?

ANSWER: β-dicarbonyl H > α-H next to carbonyl > phenol > alcohol > sp > sp2 > sp3.

TERM: Order of carboxylic acid derivative reactivity (most to least reactive)?

ANSWER: Acid chloride > anhydride > ester > amide.

TERM: Why are acid chlorides the most reactive?

ANSWER: Chloride is the best leaving group.

TERM: What determines reactivity of acid derivatives?

ANSWER: Leaving group ability.

TERM: First step of acid-catalyzed amide hydrolysis?

ANSWER: Protonate the carbonyl oxygen.

TERM: First step of Claisen or Dieckmann reactions?

ANSWER: Deprotonation of the α-hydrogen to form an enolate.

TERM: What must a Claisen condensation end with?

ANSWER: Deprotonation of the β-keto ester (due to high acidity).

TERM: What happens to tetrahedral intermediates?

ANSWER: They collapse by expelling the best leaving group.

TERM: Products of acid-catalyzed amide hydrolysis?

ANSWER: Carboxylic acid and ammonium (NH4+).

TERM: Product of LiAlH4 reduction of an amide?

ANSWER: An amine.

TERM: Product of Grignard addition to a ketone?

ANSWER: A tertiary alcohol.

TERM: What is the product of NaOH + heat on an aldol?

ANSWER: An α

TERM: What does SOCl2 followed by CH3NH2 produce from a carboxylic acid?

ANSWER: An amide.

TERM: What does CH3MgBr add to carbonyl compounds as?

ANSWER: A methyl carbanion (CH3−).

TERM: What does LDA avoid doing?

ANSWER: Does not add; only removes a proton to form an enolate.

TERM: What causes an aldol to undergo condensation?

ANSWER: Heat.

TERM: What does PCC avoid doing compared to CrO3?

ANSWER: PCC avoids overoxidizing aldehydes to acids.

TERM: What does Lindlar catalyst avoid doing?

ANSWER: Avoids reducing the alkene; stops at the cis-alkene stage.

TERM: What does H+

H2O do to acetals?

TERM: What happens when NaOH attacks an ester?

ANSWER: Ester hydrolysis (saponification) forming a carboxylate.

TERM: Why are β-dicarbonyl protons so acidic?

ANSWER: The conjugate base is stabilized by resonance with two carbonyls.

TERM: What is the driving force of Claisen condensation?

ANSWER: Final deprotonation forming a stabilized β-keto ester.

TERM: What does PBr3 do to alcohols?

ANSWER: Converts alcohols to alkyl bromides via SN2.

TERM: What does PBr3 and Br2 do to carbonyl compounds?

ANSWER: α-bromination.

TERM: What does LiAlH4 do to carboxylic acids?

ANSWER: Reduces them to primary alcohols.

TERM: What is formed when CH3MgBr reacts with formaldehyde?

ANSWER: A primary alcohol.

TERM: Do Grignards react with amides?

ANSWER: No

TERM: What is the best base for enolate formation?

ANSWER: LDA.

TERM: What type of ring does Dieckmann usually form?

ANSWER: Five- or six-membered rings.