Practice Test 4 - Organic Chemistry 1

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

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1. In the sodium-ammonia reduction of alkynes, the first electron transfer creates a radical anion. What structural feature makes internal alkynes more reactive toward this initial electron transfer compared to terminal alkynes?
2. In a detailed mechanistic study, researchers measured the rates of $S_N1$ reactions for a series of tertiary alkyl chlorides with different β-substituents: (CH₃)₃CCl, (CH₃)₂C(Et)Cl, and (CH₃)₂C(CF₃)Cl. The relative rates were found to be 1000:100:1, respectively. What is the most likely explanation for the dramatic rate variation among these structurally similar tertiary substrates?
3. A compound with the molecular formula C₈H₁₂ is treated with excess H₂ over Lindlar's catalyst to yield (Z)-cyclooctene. What is the structure of the starting compound?
4. A chemist wishes to synthesize (Z)-oct-4-ene from oct-4-yne. Which set of hydrogenation conditions is most appropriate for this specific stereochemical outcome?
5. When comparing the chair conformations of isopropylcyclohexane, the equatorial conformation is preferred over the axial by approximately 9.2 kJ/mol. This value is larger than the 7.6 kJ/mol preference shown by methylcyclohexane. What structural feature of the isopropyl group best accounts for this increased preference?
6. Predict the major product for the reaction of cyclohexene with Br₂ in methanol (CH₃OH).
7. Which of the following anions is the most stable?
8. When 3-methylcyclohex-1-ene is treated with HBr in the presence of peroxides, the major product has which structural feature?
9. A reaction coordinate diagram is plotted with Gibbs Free Energy (G) on the y-axis. The difference in free energy between the highest energy transition state and the reactants is ΔG‡, and the difference between products and reactants is ΔG_rxn. If ΔG_rxn is observed to be negative, what can be concluded with certainty?
10. Consider the following four carboxylic acids: (1) $\text{CF}_3\text{COOH}$, (2) $\text{CH}_3\text{COOH}$, (3) $\text{CCl}_3\text{COOH}$, and (4) $\text{CHF}_2\text{COOH}$. Based on inductive effects, which correctly ranks these acids from strongest to weakest?
11. When comparing the SN1 reactivity of 1-chloro-1-phenylethane and 1-chloro-1-cyclohexylethane under identical conditions, the phenyl-containing compound reacts approximately $10^4$ times faster. However, when 2-chloro-2-phenylpropane is compared to 2-chloro-2-methylpropane, the rate difference is only about $10^2$. What factor best accounts for this difference in rate enhancement?
12. A researcher has a sample of a chiral alkyne, (S)-4-methyl-1-hexyne. Which reaction will convert this alkyne to a chiral alkene with (E) geometry?
13. A reaction can form two products, X and Y. At 25 °C, the equilibrium constant K_eq for the reaction S ⇌ X is 10, and for S ⇌ Y is 100. The rate of formation of X is 50 times faster than the rate of formation of Y. What is the major product if the reaction is run at 25 °C and stopped after a very short time?
14. According to molecular orbital theory, what is the primary electronic feature that accounts for the extreme instability of a planar, 4n π-electron (anti-aromatic) system like cyclobutadiene?
15. In the E2 elimination of cis-1-bromo-2-methylcyclohexane, the major product is 3-methylcyclohexene. Why is the thermodynamically more stable Zaitsev product, 1-methylcyclohexene, only a minor product?
16. The triphenylmethyl (trityl) radical is exceptionally stable and unreactive for a free radical. What is the primary reason for its unusual stability?
17. What is the expected major product when (R)-3-methyl-1-pentyne is treated with sodium metal in liquid ammonia?
18. When 1-methylcyclohexene is treated with BH₃/THF followed by H₂O₂/OH⁻, the major product exists predominantly in which chair conformation, and why?
19. A student proposes that to maximize the yield of a kinetic product, the reaction should be run at a low temperature for a very long time. What is the primary flaw in this strategy?
20. The inductive effect describes the polarization of sigma bonds, which creates bond dipoles. Which of the following molecules has a net molecular dipole moment with a magnitude closest to zero?

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