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Ch. 9 - Alkenes II: Oxidation and Reduction
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 8, Problem 45h(x)

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (x) D2, Pd/C.
(h) Chemical structure of an alkene with a double bond, illustrating hydrogenation reaction conditions.

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1
Identify the type of reaction: The reaction involves an alkene and deuterium (D₂) in the presence of a palladium on carbon (Pd/C) catalyst. This is a catalytic hydrogenation reaction, where the double bond in the alkene is reduced to a single bond by the addition of deuterium atoms.
Understand the mechanism: In catalytic hydrogenation, the alkene π-bond interacts with the catalyst surface, allowing the D₂ molecule to dissociate into two D atoms. These D atoms are then added to the carbon atoms of the double bond in a syn addition (both deuterium atoms add to the same face of the alkene).
Determine the product: The double bond in the alkene is replaced by a single bond, and each carbon atom of the former double bond gains one deuterium atom. The stereochemistry of the product will depend on the starting alkene's structure (e.g., cis or trans).
Consider regioselectivity and stereoselectivity: Since this is a simple addition of deuterium, there is no regioselectivity to consider. However, the syn addition nature of the reaction means that the stereochemistry of the product will reflect this (e.g., if the alkene is cyclic, the deuterium atoms will add to the same face of the ring).
Write the product structure: Replace the double bond in the alkene with a single bond, and add one deuterium atom to each carbon of the former double bond. Ensure that the stereochemistry is consistent with syn addition if applicable.

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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, such as an alkene or alkyne, resulting in the formation of a saturated compound. In the presence of a catalyst like palladium on carbon (Pd/C), the reaction proceeds efficiently, converting double bonds into single bonds and increasing the saturation of the molecule.
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The definition of hydrogenation.

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). They are unsaturated compounds, which means they have fewer hydrogen atoms than their saturated counterparts (alkanes). The presence of the double bond makes alkenes more reactive than alkanes, allowing them to undergo various addition reactions, including hydrogenation.
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Catalysis

Catalysis is the process by which the rate of a chemical reaction is increased by the presence of a catalyst, which is a substance that is not consumed in the reaction. In the case of hydrogenation, palladium (Pd) acts as a catalyst, facilitating the addition of hydrogen to the alkene without being permanently altered, thus allowing the reaction to proceed more rapidly and under milder conditions.
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