Organic Chemistry 2 Quiz: Alpha Halogenation And Haloform Reaction

What this quiz covers

This quiz focuses on Alpha Halogenation And Haloform Reaction, giving you a quick way to practice the rules, question types, and explanations that matter most for Organic Chemistry 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Ester enolates are less stabilized because resonance is impossible
2. Ester ;1-hydrogens are less acidic, making enolate formation less favorable (correct answer)
3. Esters cannot form enols, so halogenation must be radical-based
4. Esters undergo only carbonyl halogenation, never ;1-substitution reactions

Question 2

1. First halogen reduces enol content by deactivating further enolization (correct answer)
2. First halogen increases enol content dramatically, causing runaway halogenation
3. Acidic media instantly cleave methyl ketones to carboxylates and $CHX_3$
4. Acid prevents any tautomerization, so halogenation must stop immediately

Question 3

1. The C-centered enolate resonance form bearing negative charge at C;1 (correct answer)
2. The O-protonated carbonyl resonance form bearing positive charge on oxygen
3. A carbocation at C;1 stabilized by hyperconjugation from halogens
4. A radical delocalized over C;1 and oxygen formed by $X_2$ homolysis

Question 4

1. Strong base in aprotic solvent to drive deprotonation equilibrium (correct answer)
2. Strong acid to protonate oxygen and generate carbocation character
3. Neutral water with no base, relying on radical chain bromination
4. Lewis acid to favor acyl substitution over deprotonation

Question 5

1. Halogenation increases ;1-hydrogen acidity, accelerating further enolate formation (correct answer)
2. Halogenation decreases ;1-hydrogen acidity, preventing additional deprotonation
3. Halogenation blocks resonance, eliminating enolate stabilization completely
4. Halogenation forces ketone hydration, diverting reaction to gem-diols

Question 6

1. Enol formation via ;1-deprotonation of the protonated carbonyl (correct answer)
2. Attack of bromide on the carbonyl carbon to form an acyl bromide
3. Rapid electrophilic capture of enol by $Br_2$ in solution
4. Radical initiation step producing $Br\cdot$ from $Br_2$ photolysis

Question 7

1. LDA in THF at low temperature to form enolate cleanly (correct answer)
2. Concentrated $HCl$ to protonate oxygen and enhance deprotonation
3. $NaBH_4$ to reduce the carbonyl before halogenation occurs
4. $AlCl_3$ to form an acylium ion for electrophilic halogenation

Question 8

1. Enolate acts as nucleophile, attacking $Br_2$ to form C;1;1;1Br bond (correct answer)
2. Enolate serves as leaving group, expelling $Br^-$ from carbonyl carbon
3. Enolate is a carbocation equivalent that attracts hydroxide strongly
4. Enolate initiates radical chain by homolysis of $Br_2$ in solution

Question 9

1. Cb1b1b1C(acyl) bond cleavage of the trihalomethyl carbinolate intermediate (correct answer)
2. C=O bond cleavage after nucleophilic addition of hydroxide to carbonyl
3. Cb1b1b1X bond cleavage to expel $X^-$ and form an alkene
4. Ob1b1b1H bond cleavage from water to generate $X_2$ electrophile

Question 10

1. 2-butanone, because it contains a $-COCH_3$ methyl ketone unit
2. Cyclohexanone, because it lacks a methyl group adjacent to carbonyl (correct answer)
3. Acetone, because it is too hindered to form an enolate
4. Acetophenone, because aryl groups prevent b1-halogenation completely

Question 11

1. Under acidic conditions, the rate of halogenation is independent of the halogen's concentration and identity.
2. Under basic conditions, it is difficult to isolate the mono-halogenated product because polyhalogenation is typically much faster.
3. Acid-catalyzed halogenation is an autocatalytic process because one of the products, HX, is an acid catalyst.
4. Under basic conditions, the rate-determining step is the nucleophilic attack of the enolate on the halogen molecule (X₂). (correct answer)

Question 12

1. The enol intermediate formed under acidic conditions is far less nucleophilic than the enolate formed under basic conditions, preventing polyhalogenation.
2. The bromine atom introduced in the first step deactivates the alpha-carbon toward further enolization in acid, but its inductive effect activates the remaining alpha-protons toward deprotonation in base. (correct answer)
3. The tetrahedral intermediate in the basic reaction is uniquely unstable and collapses via cleavage, whereas the acidic reaction proceeds through a direct SN2-like displacement mechanism.
4. Acetic acid is a weak acid that provides only catalytic turnover, leading to incomplete reaction, while excess sodium hydroxide is a strong base that drives the reaction to full polyhalogenation and cleavage.

Question 13

1. Propiophenone (Ph-CO-CH₂CH₃)
2. 1-Phenyl-2-propanone (PhCH₂-CO-CH₃) (correct answer)
3. 3-Phenylpropanal (PhCH₂CH₂CHO)
4. 4-Phenyl-2-butanone (PhCH₂CH₂-CO-CH₃)

Question 14

1. The ⁻CX₃ anion is immediately protonated by the carboxylic acid formed, which drives the cleavage step forward.
2. The three highly electronegative halogen atoms effectively stabilize the negative charge on the carbon through a strong inductive effect. (correct answer)
3. The large size of the halogen atoms creates significant steric strain in the tetrahedral intermediate, which is relieved upon cleavage.
4. The reaction is performed under strongly basic conditions, which lowers the activation energy for the departure of any anionic leaving group.

Question 15

1. One equivalent of Br₂ and catalytic HBr in acetic acid.
2. Two equivalents of Br₂ and catalytic HBr in acetic acid.
3. Two or more equivalents of Br₂ and a stoichiometric amount of NaOH. (correct answer)
4. Two equivalents of N-bromosuccinimide (NBS) and benzoyl peroxide.

Question 16

1. The first halogen atom stabilizes the enolate intermediate through resonance, making it form more quickly.
2. The halide ion (X⁻) produced in the first step acts as a catalyst for the subsequent deprotonation steps.
3. The C-X bond formed is weaker than the C-H bond it replaced, making the subsequent steps in the mechanism have a lower activation energy.
4. The electron-withdrawing inductive effect of the first halogen atom increases the acidity of the remaining α-protons, accelerating their removal by the base. (correct answer)

Question 17

1. 1.0 mole of 1,1,1-tribromoacetone and 3.0 moles of HBr
2. 0.5 moles of hexabromoacetone and 3.0 moles of NaBr
3. 1.0 mole of sodium acetate and 1.0 mole of bromoform
4. 1.0 mole of acetic acid and 1.0 mole of bromoform (correct answer)

Question 18

1. 1-Phenyl-1-propyne
2. Benzyl methyl ether
3. 4-Phenyl-3-buten-2-one (correct answer)
4. 3-Phenyl-2-propanol

Question 19

1. 2-Heptanone
2. 3-Heptanone
3. 2,4-Dimethyl-3-pentanone (correct answer)
4. 4,4-Dimethyl-2-pentanone

Question 20

1. The reaction yields butanoic acid and bromoform as the major products.
2. The reaction yields a complex mixture of mono-, di-, and tri-brominated butanones, with little to no cleavage. (correct answer)
3. The reaction cleanly produces 1-bromo-2-butanone as the sole organic product.
4. No reaction occurs because the haloform reaction requires at least 3 equivalents of halogen and 4 of base.