Question

Assuming that the mechanism for the hydrogenation of ${\mathrm{C}}_2{\mathrm{H}}_4$ given in Section 12.7 is correct, would you predict that the product of the reaction of ${\mathrm{C}}_2{\mathrm{H}}_4$ with ${\mathrm{D}}_2$ would be ${\mathrm{CH}}_2\mathrm{D}-{\mathrm{CH}}_2\mathrm{D}$ or ${\mathrm{CHD}}_2-{\mathrm{CH}}_3?$ How could the reaction of ${\mathrm{C}}_2{\mathrm{H}}_4$ with ${\mathrm{D}}_2$ be used to confirm the mechanism for the hydrogenation of ${\mathrm{C}}_2{\mathrm{H}}_4$ given in Section 12.7$?$

Short answer

Based on the mechanism given in Section 12.7 for the hydrogenation of C2H4, the predicted product of the reaction of C2H4 with D2 would be CH2D-CH2D (C2H4D2). This reaction can be used to confirm the mechanism by comparing the predicted product with the experimentally observed product. If the observed product matches the predicted CH2D-CH2D, it would support the given mechanism. If it differs, further investigation would be needed.

Step-by-step solution

Identify the Mechanism of Hydrogenation of C2H4

To solve this problem, we first need to understand the mechanism of hydrogenation of C2H4. According to Section 12.7, the reaction takes place as follows: 1. The pi bond of C2H4 reacts with one hydrogen of a dihydrogen molecule (H2) to form a C2H5 intermediate. 2. The C2H5 intermediate then reacts with the second hydrogen of the dihydrogen molecule, resulting in the final product, C2H6 (Ethane).

Predict the Product of Reaction of C2H4 with D2

Now, we need to use a similar reasoning to predict the product of the reaction between C2H4 and D2. We follow the mechanism that has been given for the hydrogenation of C2H4: 1. The pi bond of C2H4 reacts with one deuterium (D) of D2 to form a C2H4D intermediate. 2. The C2H4D intermediate reacts with the second deuterium of the D2 molecule. The predicted product would be CH2D-CH2D (C2H4D2).

Use the Reaction to Confirm the Mechanism

The reaction of C2H4 with D2 can be used to confirm the mechanism provided in Section 12.7 by observing the product obtained experimentally. If the product is CH2D-CH2D as predicted, it would support the mechanism given in Section 12.7 because the reaction followed the same pathway as the hydrogenation of C2H4. If the experimental product is different, such as CHD2-CH3, it would suggest that the mechanism for the hydrogenation of C2H4 may not be entirely correct, and further investigation would be needed.

Key concepts

C2H4

C2H4, also known as ethylene, is a fundamental organic molecule with important industrial applications. It consists of two carbon atoms connected by a double bond and each carbon atom bonded to two hydrogen atoms. This planar molecule is highly reactive due to the presence of the carbon-carbon double bond.

Ethylene is the simplest alkene and is commonly used as a starting material in various chemical synthesis processes. In hydrogenation reactions, the double bond can be converted into a single bond by adding hydrogen atoms. This process turns ethylene (C2H4) into ethane (C2H6), where each carbon is now bonded to three hydrogen atoms, making the molecule saturated.

Understanding the structure and reactivity of ethylene is crucial when studying its chemical reactions, such as hydrogenation, because the availability of active sites on the molecule allows for targeted alterations during chemical reactions.

dihydrogen reaction

A dihydrogen reaction involves the interaction of a compound with a molecule of hydrogen, symbolized as H2. In this context, we are specifically exploring the hydrogenation of C2H4, or ethylene, where H2 is involved in breaking the double bond and saturating the molecule.

During the hydrogenation process, the double bond of ethylene splits, allowing each of the two hydrogen atoms from H2 to bond to one of the carbon atoms of C2H4. This results in the transformation of the unsaturated ethylene molecule into the saturated ethane molecule. The mechanism begins with the approach of the H2 molecule towards the C2H4, where one of the H atoms forms a bond with a carbon, creating a C2H5 intermediate. Subsequently, the addition of the second hydrogen atom finalizes the reaction to form C2H6.

Dihydrogen reactions like this one are essential in industrial applications. They are used in producing everyday products, from margarine to various fuels, demonstrating their relevance and the economic importance of understanding these mechanisms.

reaction prediction

Reaction prediction in chemistry involves forecasting the product(s) of a chemical reaction based on the reactants and the given reaction mechanism. In our scenario, based on the mechanism where C2H4 undergoes hydrogenation to form ethane, we predict the outcome when deuterium (D2) replaces the dihydrogen (H2).

When C2H4 encounters D2, we anticipate a similar reaction pathway where deuterium atoms instead of hydrogen atoms bond to the ethylene molecule. Initially, one deuterium atom from D2 bonds to a carbon in C2H4, forming an intermediate. This intermediate then captures the second deuterium, yielding the product CH2D-CH2D, or simply deuterated ethane.

Proper reaction prediction is crucial for both experimental chemists and industry professionals as it helps in planning and executing synthesis reactions effectively, reducing trial and error, and ensuring efficient use of time and resources.

deuterium labeling

Deuterium labeling is a technique used in chemistry to trace chemical transformations and verify reaction mechanisms. Deuterium, a stable hydrogen isotope, is chemically identical to hydrogen but has unique properties that allow scientists to track its movement and incorporation into molecules during reactions.

In the hydrogenation mechanism for C2H4, replacing the regular hydrogen gas with deuterium (D2) facilitates a clearer observation of the reaction steps. If C2H4 reacts with D2 to produce CH2D-CH2D, this outcome confirms the original reaction pathway. This is because the deuterium atoms behave similarly to hydrogen atoms but can be more easily detected due to their mass difference.

By using deuterium labeling, researchers gain insights into reaction dynamics and can validate or refine understanding of chemical processes. This technique is invaluable for scientists working to optimize reactions in laboratory settings and industrial applications.