Question

Show reagents and experimental conditions to bring about the following transformations.

Short answer

Answer: To convert 1-butene into 2-butanol, the sequence of reagents and experimental conditions is as follows: 1. Borane (BH3) 2. Low temperatures (e.g., -78°C) for the hydroboration step 3. Hydrogen peroxide (H2O2) 4. Sodium hydroxide (NaOH) 5. Aqueous medium and room temperature for the oxidation step.

Step-by-step solution

Identify the functional groups

Examine the starting material and the product. Note any differences in functional groups. This will give an idea of the necessary reagents and conditions.

Recall previous reactions

Think back to reactions that utilize the identified functional groups. Look for reactions that either add or remove the identified functional groups in the transformation.

Combine reagents and conditions

Based on the previous reactions, combine the correct reagents and experimental conditions necessary to obtain the given transformation. Example: Given the following transformation: Starting material: 1-butene (CH2=CH-CH2-CH3) Product: 2-butanol (CH3-CH(OH)-CH2-CH3) Now, let's proceed to solving the problem through the following steps.

Identify the functional groups

In the starting material, we have an alkene (C=C double bond) while in the product, we have an alcohol (OH group).

Recall previous reactions

We know that by hydroboration-oxidation reaction, an alkene can be converted into an alcohol with anti-Markovnikov regiochemistry, which is what we need in our transformation.

Combine reagents and conditions

For hydroboration-oxidation, we use the reagents borane (BH3) followed by hydrogen peroxide (H2O2) and sodium hydroxide (NaOH) as the oxidizing agents. The experimental conditions would involve first reacting the alkene with borane at low temperatures (e.g., -78°C) and then the addition of hydrogen peroxide and sodium hydroxide in water (aqueous medium) at room temperature. Hence, the reagents and experimental conditions required for this transformation are as follows: 1. Borane (BH3) 2. Hydrogen peroxide (H2O2) 3. Sodium hydroxide (NaOH) 4. Low temperatures for the hydroboration step 5. Aqueous medium and room temperature for the oxidation step.

Key concepts

Functional Groups Identification

In organic chemistry, identifying functional groups is crucial for understanding how molecules will react. Functional groups are specific groups of atoms within molecules that have characteristic properties and dictate how a molecule will react in chemical reactions. For example, alkenes contain a C=C double bond that can undergo addition reactions, while alcohols have an -OH group that can participate in substitution and elimination reactions.

When analyzing an organic synthesis problem, start by comparing the functional groups in the starting material and the product. Pay attention to what has been added, removed, or changed. This initial step paves the way for selecting the appropriate chemical reactions and reagents to achieve the desired transformation.

Hydroboration-Oxidation Reaction

The hydroboration-oxidation reaction is a two-step process used to convert alkenes into alcohols with anti-Markovnikov selectivity, meaning the hydroxyl group attaches to the less substituted carbon atom. In the first step, hydroboration, an alkene reacts with borane (BH₃) in a syn addition, where both the hydrogen and the boron add to the same side of the double bond.

After the hydroboration, oxidation takes place. The addition of hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH) to the organoborane intermediate leads to the formation of the alcohol. This reaction is stereospecific and regioselective, making it useful for preparing alcohols from alkenes in a precise manner.

Chemical Reagents Selection

Selecting the correct chemical reagents is essential for driving an organic reaction toward the wanted product. Reagents are substances introduced to cause a chemical reaction. For the alkene to alcohol transformation, borane is the reagent that initiates hydroboration by adding across the double bond.

Then, hydrogen peroxide and sodium hydroxide are used to oxidize the borane intermediate to yield the alcohol. Keep in mind that each reagent's role is specific; borane directs the addition reaction, while hydrogen peroxide and sodium hydroxide are crucial for the oxidation step. Understanding each reagent's role guides the chemist in manipulating functional groups to achieve the desired molecular transformations.

Experimental Conditions in Organic Synthesis

The outcome of an organic reaction can be greatly influenced by experimental conditions such as temperature, solvent, concentration, and reaction time. For the hydroboration step, a low temperature, often around -78°C, is used to control the reaction rate and improve selectivity.

In contrast, the oxidation step is typically carried out at room temperature. This step often takes place in an aqueous medium, which provides the necessary conditions for the oxidation to proceed. Proper control of these experimental conditions can lead to higher yields and purity of the desired product while minimizing the creation of byproducts.

Alkene to Alcohol Transformation

The transformation of an alkene to an alcohol through hydroboration-oxidation is a widely-employed method in organic synthesis because of its specificity and reliability. This method allows for the clean synthesis of alcohols, making it a preferred route when designing pathways for complex molecule synthesis.

Following the correct protocol and reagent selection, along with controlled experimental conditions, enables chemists to achieve high selectivity and yields in such transformations. By mastering this versatile reaction, chemists can efficiently synthesize alcohols from relatively simple alkenes.