Practice Test 3 - Organic Chemistry 1

20 questions. Answer them in any order, then submit to see your score and every explanation.

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1. During the acid-catalyzed hydration of 3,3-dimethyl-1-butene, a carbocation rearrangement occurs. What is the stereochemical outcome at the carbon bearing the hydroxyl group in the major product?
2. The SN2 reaction of 1-chlorobutane is carried out separately with equimolar amounts of NaSH and NaOH in ethanol. Why is the rate of formation of 1-butanethiol significantly faster than the rate of formation of 1-butanol?
3. Borane is commercially available as a Lewis acid-base complex with tetrahydrofuran (BH₃·THF). What is the primary function of the THF in this reagent?
4. Treatment of 2-methyl-2-butene with $OsO_4$ followed by $NaHSO_3$ workup produces which stereochemical outcome?
5. Which set of reagents and conditions would be most effective for converting 2-bromobutane into 1-butene as the major product?
6. An unknown compound C5H11Br undergoes solvolysis in ethanol to produce a mixture of ethers and alkenes. The major alkene product is 2-methyl-2-butene. Which of the following structures for C5H11Br is most consistent with the formation of this alkene as the major product?
7. In which of the following substrates would a carbocation rearrangement be LEAST likely to occur during an SN1 reaction?
8. Consider the E2 reaction of 2-bromo-2,3-dimethylbutane with sodium methoxide. The Zaitsev product is 2,3-dimethylbut-2-ene, and the Hofmann product is 2,3-dimethylbut-1-ene. Which statement best predicts and explains the outcome?
9. A researcher synthesizes a compound with the molecular formula C₈H₁₆O₂ that contains two alcohol functional groups. Upon analysis, the compound is found to have exactly 4 stereoisomers. If the compound has no internal symmetry planes, how many stereocenters must it contain?
10. A nitrogen atom in a heterocyclic compound exhibits bond angles of approximately 120° and participates in a conjugated π system. However, unlike typical sp$^2$ nitrogen, this atom also has a formal positive charge. How does the positive charge affect the hybridization and geometry compared to neutral sp$^2$ nitrogen?
11. The p$K_a$ values for the two ionizable protons of malonic acid ($\text{HOOC-CH}_2\text{-COOH}$) are 2.8 and 5.7. What is the predominant species present in a solution buffered at pH 4.0?
12. A student performs E2 elimination on 2-bromo-3,3-dimethylbutane using two different bases: (1) t-BuOK in t-BuOH and (2) DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The student observes that base (1) gives primarily 3,3-dimethylbut-1-ene while base (2) gives primarily 3,3-dimethylbut-2-ene. What best explains this difference?
13. Which of the following bases is strong enough to deprotonate propyne (CH₃C≡CH, pKa ≈ 25) quantitatively, meaning the equilibrium constant (Keq) for the reaction is much greater than 1?
14. An experiment is designed to measure the rate of elimination of several 2-halo-2-methylpropane substrates when heated in ethanol. Which substrate is expected to react the fastest?
15. Consider the relative nucleophilicity of sodium phenoxide (NaOPh) and sodium cyclohexoxide. Why is cyclohexoxide a significantly stronger nucleophile?
16. When (Z)-3-methylpent-2-ene undergoes acid-catalyzed hydration ($H_2SO_4/H_2O$), what is the expected major product considering both regiochemistry and potential rearrangements?
17. A student is asked to predict the major product when (Z)-2-butene reacts with HBr in the presence of peroxides. They correctly identify that anti-Markovnikov addition will occur, but then claim the product will be optically active. What is the flaw in their reasoning?
18. 1-chlorocyclohexene is exceptionally unreactive towards substitution and elimination reactions under typical SN1, SN2, E1, or E2 conditions. Which factor provides the best explanation for this low reactivity?
19. A student incorrectly draws the mechanism for the reaction of tert-butyl bromide with water. They show a single step with two curved arrows: one from a lone pair on the oxygen of water to the tertiary carbon, and one from the C-Br bond to the bromine atom. Why is this depiction mechanistically incorrect?
20. To achieve anti-Markovnikov hydration of 1-hexene with syn stereochemistry, which reagent sequence should be employed?

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