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Chapter 11: Problem 77

Assuming that the mechanism for the hydrogenation of \(\mathrm{C}_{2} \mathrm{H}_{4}\) given in Section \(11-7\) 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 \(11-7 ?\)

Short Answer

Expert verified
Based on the given hydrogenation mechanism of C2H4, the predicted product of the reaction between C2H4 and D2 is \(CH_2D-CH_2D\). The reaction with D2 can be used to confirm the mechanism by comparing the predicted product with the actual product obtained experimentally. If the observed product matches the predicted \(CH_2D-CH_2D\), it supports the validity of the electrophilic addition mechanism given in Section 11-7.

Step by step solution

01

Understand the hydrogenation mechanism of C2H4

The hydrogenation mechanism of C2H4, as described in Section 11-7, is an electrophilic addition reaction that proceeds through a three-membered ring transition state. The mechanism can be briefly summarized as follows: 1. H2 molecule is adsorbed on the metal catalyst surface, splitting into two H atoms. 2. C2H4 molecule is adsorbed on the metal catalyst surface, polarizing the pi-bond into a sigma bond. 3. One H atom from the metal surface reacts with the C atom of C2H4 at the positively charged end. 4. Another H atom from the metal surface reacts with the other C atom of C2H4. The overall reaction is: C2H4 + H2 -> C2H6
02

Predict the reaction product between C2H4 and D2

Now, we need to apply this hydrogenation mechanism to the reaction between C2H4 and D2. Replacing H2 with D2 in the mechanism: 1. D2 molecule is adsorbed on the metal catalyst surface, splitting into two D atoms. 2. C2H4 molecule is adsorbed on the metal catalyst surface, polarizing the pi-bond into a sigma bond. 3. One D atom from the metal surface reacts with the C atom of C2H4 at the positively charged end. 4. Another D atom from the metal surface reacts with the other C atom of C2H4. The overall reaction is: C2H4 + D2 -> "\(CH_2D-CH_2D\)" So, based on the given mechanism, the product of the reaction between C2H4 and D2 is CH2D-CH2D.
03

Explain how the reaction with D2 can confirm the hydrogenation mechanism for C2H4

The reaction of C2H4 with D2 can be used to confirm the mechanism for the hydrogenation of C2H4 by comparing the predicted product with the actual product obtained from the reaction. If the experimentally observed product matches the predicted product (CH2D-CH2D), it supports the validity of the electrophilic addition mechanism given in Section 11-7. Moreover, if the CHD2-CH3 product was formed instead, it would suggest a different mechanism, like a 1,2-hydride (or deuteride) shift, indicating the need for reevaluating the proposed mechanism for the hydrogenation of C2H4.

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Most popular questions from this chapter

A certain reaction has the following general form: $$\mathrm{aA} \longrightarrow \mathrm{bB}$$ At a particular temperature and \([\mathrm{A}]_{0}=2.80 \times 10^{-3} \mathrm{M},\)concentration versus time data were collected for this reaction, and a plot of \(1 /[\mathrm{A}]\) versus time resulted in a straight line with a slope value of \(+3.60 \times 10^{-2} \mathrm{L} / \mathrm{mol} \cdot \mathrm{s}\) a. Determine the rate law, the integrated rate law, and the value of the rate constant for this reaction. b. Calculate the half-life for this reaction. c. How much time is required for the concentration of A to decrease to \(7.00 \times 10^{-4} \mathrm{M} ?\)

The activation energy of a certain uncatalyzed biochemical reaction is \(50.0 \space\mathrm{kJ} / \mathrm{mol} .\) In the presence of a catalyst at \(37^{\circ} \mathrm{C}\) the rate constant for the reaction increases by a factor of \(2.50 \times 10^{3}\) as compared with the uncatalyzed reaction. Assuming the frequency factor \(A\) is the same for both the catalyzed and uncatalyzed reactions, calculate the activation energy for the catalyzed reaction.

The central idea of the collision model is that molecules must collide in order to react. Give two reasons why not all collisions of reactant molecules result in product formation.

In the Haber process for the production of ammonia, $$\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)$$ what is the relationship between the rate of production of ammonia and the rate of consumption of hydrogen?

Two isomers \((A \text { and } B)\) of a given compound dimerize as follows: $$\begin{aligned} &2 \mathrm{A} \stackrel{k_{1}}{\longrightarrow} \mathrm{A}_{2}\\\ &2 \mathrm{B} \stackrel{k_{2}}{\longrightarrow} \mathrm{B}_{2} \end{aligned}$$ Both processes are known to be second order in reactant, and \(k_{1}\) is known to be 0.250 \(\mathrm{L} / \mathrm{mol} \cdot \mathrm{s}\) at \(25^{\circ} \mathrm{C} .\) In a particular experiment \(\mathrm{A}\) and \(\mathrm{B}\) were placed in separate containers at \(25^{\circ} \mathrm{C}\) where \([\mathrm{A}]_{0}=1.00 \times 10^{-2} \mathrm{M}\) and \([\mathrm{B}]_{0}=2.50 \times 10^{-2} \mathrm{M} .\) It was found that after each reaction had progressed for 3.00 min, \([\mathrm{A}]=3.00[\mathrm{B}] .\) In this case the rate laws are defined as $$\begin{array}{l} \text { Rate }=-\frac{\Delta[\mathrm{A}]}{\Delta t}=k_{1}[\mathrm{A}]^{2} \\ \text { Rate }=-\frac{\Delta[\mathrm{B}]}{\Delta t}=k_{2}[\mathrm{B}]^{2} \end{array}$$ a. Calculate the concentration of \(\mathrm{A}_{2}\) after 3.00 min. b. Calculate the value of \(k_{2}\) c. Calculate the half-life for the experiment involving A.
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