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Chapter 11: Problem 69

The compound \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{3}\) is hydrogenated to an alkene using platinum as the catalyst. If the product is the pure cis isomer, what can you deduce about the mechanism?

Short Answer

Expert verified
The mechanism involves syn addition. This means that both hydrogens are added from the same side of the molecule, resulting in the cis isomer. The platinum catalyst facilitates the addition of hydrogens on the same side as it holds the molecule in a particular orientation during the reaction process.

Step by step solution

01

Understand the Type of Reaction

First, we need to understand that the reaction given is a hydrogenation reaction. Here, the acetylenic compound is hydrogenated to form an alkene in presence of platinum catalyst. Hydrogenation is a reduction reaction in organic chemistry where hydrogen is added across the double or triple bond.
02

Identify the type of Isomerism

Cis-trans isomerism (also called geometric isomerism) is a form of stereoisomerism describing the orientation of functional groups within a molecule. A cis isomer is an isomer where the main functional groups are on the same side of the molecule. In this case, the product is a pure cis isomer.
03

Deduce the Mechanism

In a hydrogenation reaction, if the product is purely the cis isomer, it suggests that the reaction mechanism involves syn addition. In syn addition, both hydrogens are added to the same side of the molecule. This is supported by the use of a platinum catalyst which allows for the addition of hydrogens on the same face of the molecule. This mechanism is also often referred to as cis addition.

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Most popular questions from this chapter

Draw structures for these compounds: (a) cyclopentane, \((\) b) \(c i s-2\) -butene, \((\) c) 2 -hexanol, (d) 1,4 -dibromobenzene, (e) 2 -butyne.

Given these data $$\begin{array}{c}\mathrm{C}_{2} \mathrm{H}_{4}(g)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) \\\\\Delta H^{\circ}=-1411 \mathrm{~kJ} / \mathrm{mol} \\\2 \mathrm{C}_{2} \mathrm{H}_{2}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) \\\\\Delta H^{\circ}=-2599 \mathrm{~kJ} / \mathrm{mol} \\\\\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) \\\\\Delta H^{\circ}=-285.8 \mathrm{~kJ} / \mathrm{mol}\end{array}$$ calculate the heat of hydrogenation for acetylene: $$\mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g)$$

Write the structural formulas for these organic compounds: (a) 3 -methylhexane, (b) 1,3,5 -trichlorocyclohexane, (c) 2,3-dimethylpentane, (d) 2-bromo4 -phenylpentane, (e) 3,4,5 -trimethyloctane.

Draw all the possible structural isomers for the molecule having the formula \(\mathrm{C}_{7} \mathrm{H}_{7} \mathrm{Cl}\). The molecule contains one benzene ring.

Isopropyl alcohol is prepared by reacting propene \(\left(\mathrm{CH}_{3} \mathrm{CHCH}_{2}\right)\) with sulfuric acid, followed by treatment with water. (a) Show the sequence of steps leading to the product. What is the role of sulfuric acid? (b) Draw the structure of an alcohol that is an isomer of isopropyl alcohol. (c) Is isopropyl alcohol a chiral molecule? (d) What property of isopropyl alcohol makes it useful as a rubbing alcohol?
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