Chemistry
Workshops
Chapter 15 Workshop Problems
Aldehydes and Ketones: Synthesis and Nucleophilic Additions
1. a. Discuss the similarities and differences in the structures and reactivities of the double bonds of 2-methylpropene and 2-propanone.
b. With part a in mind, account for the following observations. Identify the nucleophile and the electrophile for the first step of each reaction.
2. Write detailed electron-pushing mechanisms that explain the stated observations.
a. The following reaction occurs rapidly at pH = 5 but fails at pH = 1.
b. Acetone can be labeled with 18O either acidic or basic solution. The labeling of acetone with 18O is catalyzed by both acid and base.
3. Propose structures for the lettered compounds.
a. Compound A, C9H12O, was optically active, did not give a precipitate with 2,4-dinitrophenylhydrazine, showed a broad IR band at 3400 cm-1, and was readily oxidized to B, C9H10O, with aqueous chromic acid (H2CrO4) at room temperature. When A was refluxed with chromic acid, benzoic acid was obtained. Compound B showed strong IR absorption at 1670 cm-1 but none at 3400 cm-1 and reacted with 2,4-dinitrophenylhydrazine reagent to give C. When B was reacted with EtMgBr followed by aqueous work up, compound D was obtained. D did not react with chromic acid reagent at room temperature, and showed an IR band at 3400 cm-1. B and D were optically inactive and could not be resolved.
b. Compound X, C8H14O, fails to give a silver mirror when treated with Ag(NH3)2+ . Treatment of the compound with Zn(Hg)/HCl produced 1,1-dimethylcyclohexane. The infrared spectrum exhibited strong absorption at 1710 cm-1 and the proton-decoupled 13C NMR spectrum exhibited five peaks.
4. When 2,2-dimethoxypropane is mixed with n-butanol and some p-toluenesulfonic acid in benzene, the equilibrium shown below is established. The lowest boiling component of this mixture is methanol. Provide a reasonable mechanism for the reaction and suggest an experimental technique that could be used to shift the equilibrium to the right and thus make the reaction useful for synthesizing the dibutylketal. (Note: There is no water present. Therefore, the reaction does NOT proceed by hydrolysis of the ketal to acetone.)
5. Pinacol rearrangement is a reaction that produces carbonyl compounds. Give a mechanism for the following reaction:
The following reaction gives only one product as shown.
What are the other two possible products? Explain the observed selectivity.
