Textbook Question
Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (ix) H2, Pd/C; and (x) D2, Pd/C.
(f)
10. Addition Reactions
Hydrogenation
6:37 minutesProblem 87k,l
Textbook Question
Draw the products of the following reactions. If the products can exist as stereoisomers show what stereoisomers are formed.
k. (Z)-3,4-dimethyl-3-hexene + H2, Pd/C
l. (E)-3,4-dimethyl-3-hexene + H2, Pd/C
Verified step by step guidance1
Step 1: Understand the reaction type. The reaction involves the addition of hydrogen (H₂) to an alkene in the presence of a catalyst (Pd/C). This is a catalytic hydrogenation reaction, which converts alkenes into alkanes by breaking the π-bond and adding hydrogen atoms to the carbons involved in the double bond.
Step 2: Analyze the starting materials. For (Z)-3,4-dimethyl-3-hexene, the double bond is in the Z-configuration, meaning the higher-priority groups on each carbon of the double bond are on the same side. For (E)-3,4-dimethyl-3-hexene, the higher-priority groups are on opposite sides of the double bond.
Step 3: Predict the product of hydrogenation. In catalytic hydrogenation, the double bond is completely reduced to a single bond, and two hydrogen atoms are added to the carbons that were part of the double bond. The resulting product will be a saturated alkane. Since the reaction occurs on a flat metal surface, the addition of hydrogen is syn (on the same side).
Step 4: Consider stereoisomerism. In this case, the product of hydrogenation will not have stereoisomers because the resulting alkane does not contain any stereogenic centers. The double bond is fully reduced, and the molecule becomes a simple alkane with no chiral centers.
Step 5: Draw the products. For both (Z)-3,4-dimethyl-3-hexene and (E)-3,4-dimethyl-3-hexene, the product will be the same: 3,4-dimethylhexane. The stereochemistry of the starting material does not affect the final product in this reaction because the double bond is completely reduced.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrogenation
Hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to an unsaturated compound, typically an alkene or alkyne, in the presence of a catalyst such as palladium on carbon (Pd/C). This process converts double or triple bonds into single bonds, resulting in saturated hydrocarbons. Understanding hydrogenation is crucial for predicting the products of the given reactions.
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Stereoisomerism
Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. In the context of alkenes, stereoisomers can arise from the presence of double bonds, leading to cis/trans or E/Z configurations. Recognizing the potential for stereoisomers is essential when determining the products of the reactions involving (Z)- and (E)-alkenes.
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Alkene Reactivity
Alkenes are reactive due to the presence of a carbon-carbon double bond, which can undergo various reactions, including addition reactions. The reactivity of alkenes is influenced by their substitution pattern, which affects the stability of the intermediates formed during reactions. Understanding the reactivity of alkenes helps in predicting the outcome of the hydrogenation reactions presented in the question.
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