Question

Provide syntheses for the following molecules, free of other isomers. You must use alkynes containing no more than four carbon atoms as starting materials. You may use inorganic reagents of your choice and other organic reagents containing no more than two carbon atoms. Mechanisms are not required.

Short answer

Choose alkynes with max four carbons, define steps including hydrohalogenation or hydration using permitted reagents, and verify the synthesis.

Step-by-step solution

- Identify the Target Molecules

List the molecules that need to be synthesized and ensure the reactants and products use only the specified reagents.

- Determine the Starting Alkyne

Select an alkyne with no more than four carbon atoms that can be used as the starting material for each target molecule.

- Choose Reagents

Identify inorganic reagents and organic reagents (containing no more than two carbon atoms) that will be needed for each synthesis.

- Plan the Reaction Steps

Outline the reaction steps required to convert the selected alkyne into the target molecule. Ensure the steps are clear and direct. Use common reactions like hydrohalogenation, hydrogenation, halogenation, hydration, etc.

- Verify the Synthesis

Double-check the synthesis paths to ensure no other isomers are produced and that all the required reagents fit within the provided guidelines.

Key concepts

Alkyne Reactions

Alkyne reactions form the backbone of organic synthesis starting from alkynes. Alkynes, which are hydrocarbons with a carbon-carbon triple bond, can undergo various reactions, altering their structure significantly. For example, hydrohalogenation can add hydrogen halides to alkynes, producing alkenes or alkanes depending on the amount of reagent used. Hydrogenation adds hydrogen to an alkyne, converting it into an alkene or an alkane through partial or full hydrogenation, respectively.
Other important reactions include halogenation (addition of halogens), hydration (adding water), and oxidation-reduction reactions. Each reaction type provides a different pathway to transform alkynes into desired products.
Understanding these key reactions is crucial as they help devise synthesis routes for complex molecules. The choice of reagents and reaction conditions will decide the final product's structure and purity, essential for achieving isomer specificity.

Organic Reagents

Organic reagents play a pivotal role in transforming alkyne starting materials into target molecules. In synthesis, the choice of reagents is limited by the exercise's constraints to molecules with no more than two carbon atoms.
Organic reagents you might encounter include:

• Ethylene glycol (for the formation of protective groups)
• Ethanol (as a solvent or a nucleophilic reagent)
• Formal suits such as formic acid (as a formylating agent).

In addition to these, various small-molecule alkylating agents or nucleophiles can help add functional groups or chains to the alkyne substrate.
The proper selection and application of these small organic reagents will guide you in the successful conversion of alkyne starting materials into the desired end products while staying within the given limits.

Synthesis Pathways

Planning synthesis pathways involves strategically outlining the steps needed to achieve the desired compound from the starting material. Begin by identifying the target molecule and determine the possible steps to achieve it. This includes choosing the right reactions at each step while ensuring that the molecules generated in-between are stable and manageable.
For alkyne-based syntheses:

• Identify intermediate steps involving addition or modification reactions, such as hydrohalogenation or hydrogenation.
• Use functional group transformations for diversification, like converting an alkyne to an alcohol via hydration.
• Break down complex transformations into simpler, more manageable steps.

Organizing these steps logically ensures clarity and achieves the end goal effectively, eliminating unwanted isomers as per the exercise's demands. Detailed planning can prevent common issues like unwanted side reactions or by-products.

Isomer Specificity

Isomer specificity is essential when synthesizing molecules to ensure that only the desired product forms, avoiding any unintended isomers. This specificity relies heavily on the careful selection of reagents and reaction conditions. For example:

• Using steric hindrance or selective reagents can promote specific molecular geometries.
• Regioselectivity can be achieved by controlling reagent addition or through catalyst choice.
• Stereoselectivity ensures the resulting molecule has the desired configuration, requiring careful consideration during addition reactions.

Achieving isomer specificity often implies a deeper understanding of reaction mechanisms and the potential spatial arrangements of the reactants and products. Ensuring that synthetic routes avoid conditions favouring multiple products is key to obtaining pure compounds from alkyne-based syntheses.