For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (iii) Na⁰ , NH₃ (liquid), ―33°C . If you expect two products, show both.
(c)

Verified step by step guidance

1. Identify the reaction type: The given reagents (Na⁰, NH₃ (liquid), ―33°C) indicate a dissolving metal reduction. This reaction is used to reduce alkynes to trans-alkenes.
2. Understand the mechanism: In a dissolving metal reduction, sodium donates an electron to the alkyne, forming a radical anion. This is followed by protonation from ammonia, and the process repeats to form a trans-alkene.
3. Determine the starting alkyne structure: Analyze the structure of the alkyne provided in part (c) to identify the triple bond and any substituents attached to it.
4. Predict the product(s): The triple bond in the alkyne will be reduced to a double bond, specifically forming a trans-alkene. If the alkyne is symmetrical, only one product will form. If it is asymmetrical, two possible trans-alkenes may form due to different substituent arrangements.
5. Draw the product(s): Represent the trans-alkene(s) with the substituents on opposite sides of the double bond. Ensure the stereochemistry is clear and consistent with the reaction mechanism.

Key Concepts

Alkynes

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond (C≡C). They are unsaturated compounds and can undergo various reactions, including addition and reduction. Understanding the structure and reactivity of alkynes is crucial for predicting the products formed during chemical reactions.

Reduction Reactions

Reduction reactions involve the gain of electrons or the decrease in oxidation state by a molecule. In the context of alkynes, treatment with sodium (Na⁰) in liquid ammonia (NH₃) at low temperatures typically leads to the reduction of the triple bond to a double bond, forming alkenes. This process is essential for understanding how alkynes can be transformed into other organic compounds.

Stereochemistry of Alkenes

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. When alkynes are reduced to alkenes, the resulting double bond can exhibit cis/trans (E/Z) isomerism, depending on the substituents attached to the double bond. Recognizing the potential for different stereoisomers is important for predicting the products of the reaction.