Question

Show how to synthesize the following alcohol using 1-bromopropane, propanal, and ethylene oxide as the only sources of carbon atoms.

Short answer

Please provide the structure of the target alcohol to be synthesized.

Step-by-step solution

Determination of the target alcohol structure

The exercise does not specify the structure of the target alcohol. Please provide the structure of the alcohol to be synthesized.

Assess the starting materials

Once the alcohol structure is known, assess the starting materials provided: 1. 1-bromopropane: CH3-CH2-CH2-Br 2. Propanal: CH3-CH2-CHO 3. Ethylene oxide: CH2-CH2 with an oxygen between the two carbons forming a 3-membered ring (epoxide)

Identify possible reactions

Identify possible reactions to connect these starting materials, depending on the molecular structure of the target alcohol. Some possible reactions include: 1. Nucleophilic substitution (SN2) - For example, reacting 1-bromopropane with an appropriate nucleophile. 2. Grignard reagent formation - Turning 1-bromopropane into a Grignard reagent that can react with a carbonyl group, such as propanal. 3. Epoxide ring opening - Reacting ethylene oxide with a suitable nucleophile or base to open the ring. 4. Reduction of propanal - Converting propanal into an alcohol by reduction.

Design a synthetic route

Once the target alcohol is known, design a synthetic route based on the possible reactions mentioned above, considering limitations in the available starting materials.

Describe the step-by-step synthesis plan

For each step of the synthetic route, describe the reaction conditions and the specific reagents needed to achieve the desired transformation. This will form a step-by-step guide for the synthesis of the target alcohol using 1-bromopropane, propanal, and ethylene oxide as the only carbon atom sources.

Key concepts

Nucleophilic Substitution (SN2) Reactions

Nucleophilic substitution reactions, especially the SN2 mechanism, are fundamental in organic chemistry for creating new bonds while a leaving group is displaced. In these reactions, the nucleophile is the 'attacker' with a lone pair of electrons, and the substrate typically has a decent leaving group such as a halide. In the SN2 reaction, the nucleophile attacks from the backside, resulting in an inversion of configuration at the carbon center, if the carbon is chiral. This is essential to consider when synthesizing molecules with specific stereochemistry.

Regarding the task at hand, 1-bromopropane serves as an excellent substrate for an SN2 reaction. The bromine atom is a good leaving group, and its displacement by a nucleophile will result in the formation of a new carbon-nucleophile bond. This kind of reaction is often used to extend carbon chains or introduce functional groups necessary for further synthesis steps.

Grignard Reagent Formation

Grignard reagents are powerful tools for forming carbon-carbon bonds and are made by reacting alkyl halides with magnesium in dry ether. They act as carbanions, with the carbon bearing a partial negative charge, allowing them to attack electrophilic carbon atoms, particularly those found in carbonyl groups.

A critical application for our synthetic problem is the transformation of 1-bromopropane into a Grignard reagent. This reagent can then be used to react with propanal, an aldehyde, to form a secondary alcohol after hydrolysis. The choice of using a Grignard reagent offers both flexibility and specificity in the synthesis of alcohols with varying complexities. For students, visualizing how the Grignard reagent attacks the carbonyl carbon and understanding the nuances of the reaction conditions, such as the necessity of a dry environment, are crucial to mastering its use in synthesis.

Epoxide Ring Opening

Epoxides are three-membered cyclic ethers that are high in ring strain, making them susceptible to nucleophilic attack and thus useful in organic synthesis. The opening of an epoxide ring can occur under either acidic or basic conditions, depending on the desired outcome in terms of regioselectivity and stereochemistry.

In the synthesis problem, ethylene oxide is our epoxide that can be opened to form a new carbon-oxygen bond. This is particularly useful for extending the carbon chain further, allowing us to manipulate the structure to our specific needs. Understanding the epoxide ring opening is essential for students as it highlights how to control the formation of new chiral centers, a pivotal aspect in creating complex molecules with the correct 3D orientation.

Reduction of Propanal

The reduction of carbonyl compounds like aldehydes to alcohols is a key step in synthetic organic chemistry. For reducing propanal to propanol, there are various reducing agents, such as sodium borohydride (NaBH₄) or lithium aluminum hydride (LiAlH₄). The reduction of propanal involves the addition of a hydride ion (H^-) to the carbonyl carbon, forming an alkoxide intermediate, which upon protonation yields the alcohol.

In our synthetic scheme, the reduction step is vital as it provides the alcohol functional group necessary for achieving the target molecule. It's important for students to comprehend not only the mechanistic pathway but also when to choose one reducing agent over another, considering aspects such as reactivity and compatibility with other functional groups present in the molecule.