Test: Reaction Mechanism Level - 7 - Chemistry MCQ

All four reactions produce benzaldehyde.

To determine how many compounds can form stable hydrates, consider the electron-withdrawing groups (EWGs) attached to the carbonyl carbon. EWGs increase the carbonyl’s electrophilicity, stabilizing the hydrate.

1. CF₃-CHO: The trifluoromethyl group is a strong EWG, stabilizing the hydrate. Forms a stable hydrate.

2. F₅C-CHO: Pentafluoromethyl is highly electron-withdrawing, enhancing electrophilicity. Forms a stable hydrate.

3. CCl₃-CHO: Trichloromethyl is a strong EWG, making the hydrate stable.

4. Benzaldehyde: The phenyl group is weakly withdrawing. Does not form a stable hydrate.

5. Cyclic dicarbonyl compound: Intramolecular hydrogen bonding stabilizes its hydrate. Forms a stable hydrate.

6. Diphenyl compound (Ph₂CO₂): The bulky phenyl groups reduce hydration tendency. Does not form a stable hydrate.

Final Answer: 4 compounds form stable hydrates.

An SN1 reaction (Substitution Nucleophilic Unimolecular) is a type of nucleophilic substitution reaction where the rate-determining step involves the formation of a carbocation intermediate. The key features of an SN1 reaction are:

1. Reaction 1:

   • Reactant: 1-chlorobutane with NaCl in DMSO.
   • Mechanism: DMSO (dimethyl sulfoxide) is a polar aprotic solvent, favoring SN2 mechanism, as it does not stabilize the carbocation intermediate needed for SN1.
   • Conclusion: SN2 reaction, not SN1.

2. Reaction 2:

   • Reactant: Cyclohexyl chloride with water.
   • Mechanism: Water is a polar protic solvent, which stabilizes the carbocation intermediate. Cyclohexyl chloride can form a stable carbocation, so this is an SN1 reaction.
   • Conclusion: SN1 reaction.

3. Reaction 3:

   • Reactant: 1-chlorocyclohexane with ethanol.
   • Mechanism: Ethanol is a polar protic solvent, which favors the SN1 mechanism. The carbocation intermediate that forms is stable.
   • Conclusion: SN1 reaction.

4. Reaction 4:

   • Reactant: Methyl chloride with NaOCH3 in DMF.
   • Mechanism: DMF is a polar aprotic solvent, which favors SN2 reactions. Since methyl chloride is a good electrophile, it is more likely to undergo SN2 rather than SN1.
   • Conclusion: SN2 reaction, not SN1.

5. Reaction 5:

   • Reactant: 1,2-dichlorocyclohexane with NaSMe in DMA.
   • Mechanism: DMA is a polar aprotic solvent, which favors SN2 reactions. The structure likely leads to an SN2 mechanism.
   • Conclusion: SN2 reaction, not SN1.

6. Reaction 6:

   • Reactant: 1-chlorocyclohexane with NaI in acetone.
   • Mechanism: Acetone is a polar aprotic solvent, favoring SN2 reactions. The carbon center does not support SN1.
   • Conclusion: SN2 reaction, not SN1.

7. Reaction 7:

   • Reactant: Phenyl tosylate with NaOH.
   • Mechanism: Phenyl tosylate is a good leaving group, but the carbocation formed after leaving would be highly unstable, making SN1 unlikely. Since NaOH is a strong nucleophile, SN2 is more favorable.
   • Conclusion: SN2 reaction, not SN1.

8. Reaction 8:

   • Reactant: Methyl alcohol with concentrated HI.
   • Mechanism: HI is a strong nucleophile and polar protic solvent, which favors SN1 reactions when the carbocation intermediate is stable.
   • Conclusion: SN1 reaction.

Total SN1 Reactions:

There are 3 SN1 reactions in the given sequence.

Answer: 3 SN1 reactions.