Devise syntheses of the following three compounds, starting in each case with any alkene that contains four carbons or fewer. You do not have to write mechanisms, although at this point it may be very helpful for you to do so. $$ \left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH} \quad\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH} \quad \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHOHCH}_{3} $$

Alkenes are organic compounds characterized by the presence of a carbon-carbon double bond (C=C). These double bonds make alkenes reactive and versatile, essential in organic synthesis. They react with various reagents, allowing chemists to construct complex molecules from simpler ones. The general formula for alkenes is \(\text{C}_n\text{H}_{2n}\). For example, ethene (C2H4) is the simplest alkene.

When planning a synthesis, selecting the right alkene is crucial. Alkenes with four or fewer carbons, like propene or 1-butene, are commonly used starting materials. These small alkenes can undergo various additions to form a wide range of products.

Choosing the appropriate alkene and understanding how it can be transformed helps streamline the synthesis process. Alkenes can be functionalized to form alcohols, ethers, and more, serving as the foundation for creating more complex organic compounds.

Hydroboration-oxidation is a two-step reaction that converts alkenes into alcohols. First, the alkene undergoes hydroboration, where borane (BH3) adds across the double bond. This step occurs in a syn addition, meaning both the boron and hydrogen atoms add to the same side of the double bond.

The second step is oxidation, where the organoborane intermediate is oxidized to an alcohol using hydrogen peroxide (H2O2) and sodium hydroxide (NaOH). This step replaces the boron atom with a hydroxyl group (OH), resulting in the formation of an alcohol.

One significant feature of hydroboration-oxidation is its anti-Markovnikov selectivity. This means the hydroxyl group attaches to the less substituted carbon atom of the original double bond. This selectivity provides a valuable method for synthesizing alcohols with specific regiochemistry.

• Example: Synthesizing isopropanol from propene involves hydroboration with BH3, followed by oxidation to form the alcohol.
• Application: In the step-by-step solution, hydroboration-oxidation is used to make \((\text{CH}_3)_2\text{CHOH}\) and \(\text{CH}_3\text{CH}_2\text{CHOHCH}_3\).

Oxymercuration-demercuration is another method for converting alkenes into alcohols, but it follows a different mechanism compared to hydroboration-oxidation. In this two-step reaction, the first step is oxymercuration. Here, the alkene reacts with mercuric acetate (Hg(OAc)2) in water, leading to the formation of a mercurinium ion intermediate.

Water then attacks the more substituted carbon of the intermediate, breaking the ring and attaching a hydroxyl group (OH) to this carbon, and an acetate group remains bonded to a mercury atom on the other carbon.

The second step, demercuration, removes the mercury using sodium borohydride (NaBH4), which replaces the mercury with a hydrogen atom. This step completes the formation of the alcohol.

Oxymercuration-demercuration follows Markovnikov's rule, meaning the hydroxyl group attaches to the more substituted carbon atom of the double bond.

• Example: Synthesizing tert-butanol from 2-methylpropene involves oxymercuration to form an organomercury intermediate, followed by demercuration to yield the alcohol.
• Application: In the step-by-step solution, this reaction is used to synthesize \( (\text{CH}_3)_3\text{COH} \) from isobutylene.