Question

Using condensed structural formulas, write a balanced chemical equation for each of the following reactions: (a) hydrogenation of cyclohexene; (b) addition of \(\mathrm{H}_{2} \mathrm{O}\) to trans-2-pentene using \(\mathrm{H}_{2} \mathrm{SO}_{4}\) as a catalyst (two products); (c) reaction of 2 -chloropropane with benzene in the presence of \(\mathrm{AlCl}_{3}\)

Short answer

(a) \(C_6H_{10} + H_2 \rightarrow C_6H_{12}\) (b) \(C_5H_{10} + H_2O \rightarrow C_5H_{12}O + C_5H_{12}O\) (c) \(C_6H_6 + C_3H_7Cl \rightarrow C_9H_{10} + HCl\)

Step-by-step solution

Reaction (a): Hydrogenation of Cyclohexene

For this reaction, we need to add hydrogen to cyclohexene: \(Cyclohexene + H_2 \rightarrow Cyclohexane\) To write this down with condensed structural formulas and ensure it is balanced, we will use the following formulas: Cyclohexene: \(C_6H_{10}\), Cyclohexane: \(C_6H_{12}\), Hydrogen: \(H_2\). Therefore, the balanced equation is: \(C_6H_{10} + H_2 \rightarrow C_6H_{12}\)

Reaction (b): Addition of Water to trans-2-Pentene

For this reaction, we need to add water across the double bond of trans-2-pentene, which results in two products due to the presence of an asymmetric carbon: \(trans-2-Pentene + H_2O \rightarrow 2-Pentanol \ (product \ 1) + 3-Pentanol \ (product \ 2)\) To write this down with condensed structural formulas and ensure it is balanced, we will use the following formulas: trans-2-Pentene: \(C_5H_{10}\), 2-Pentanol: \(C_5H_{12}O\), 3-Pentanol: \(C_5H_{12}O\), Water: \(H_2O\). Therefore, the balanced equation is: \(C_5H_{10} + H_2O \rightarrow C_5H_{12}O + C_5H_{12}O\)

Reaction (c): Reaction of 2-Chloropropane with Benzene

This is a Friedel-Crafts alkylation reaction, and we need to add the alkyl group from 2-chloropropane to the benzene ring: \(Benzene + 2-Chloropropane \rightarrow 1-Phenylpropane\) To write this down with condensed structural formulas and ensure it is balanced, we will use the following formulas: Benzene: \(C_6H_6\), 2-Chloropropane: \(C_3H_7Cl\), 1-Phenylpropane: \(C_9H_{10}\), Hydrogen chloride: \(HCl\). Therefore, the balanced equation is: \(C_6H_6 + C_3H_7Cl \rightarrow C_9H_{10} + HCl\)

Key concepts

Hydrogenation

Hydrogenation is a fundamental reaction in organic chemistry that involves the addition of hydrogen (\(H_2\)) to an unsaturated compound, such as an alkene or alkyne, converting it into a more saturated form. This process typically requires a catalyst, often a transition metal like palladium, platinum, or nickel. In our exercise, we have hydrogenation of cyclohexene.

In this reaction, cyclohexene (\(C_6H_{10}\)) is converted into cyclohexane (\(C_6H_{12}\)) by the addition of hydrogen gas (\(H_2\)). The balanced chemical equation is:

• \(C_6H_{10} + H_2 \rightarrow C_6H_{12}\)

This equation shows the hydrogen effectively saturates the carbon-carbon double bond, resulting in a fully saturated cyclic hydrocarbon. Hydrogenation is crucial in various industries, including food processing, where it converts liquid oils into solid fats, and in fuel processing.

Friedel-Crafts Alkylation

The Friedel-Crafts alkylation is a reaction used to introduce an alkyl group into an aromatic ring, such as benzene. This reaction involves the use of a Lewis acid catalyst like aluminum chloride (\(AlCl_3\)). In this exercise, benzene reacts with 2-chloropropane in the presence of \(AlCl_3\).

The reaction promotes the formation of a carbocation from the alkyl halide, which then adds to the benzene ring, forming an alkyl-benzene derivative. The balanced equation for this specific reaction is:

• \(C_6H_6 + C_3H_7Cl \rightarrow C_9H_{10} + HCl\)

The product, 1-phenylpropane (\(C_9H_{10}\)), results from the attachment of a propyl group to the aromatic compound, making Friedel-Crafts alkylation useful in synthesizing complex aromatic compounds in pharmaceuticals and materials science.

Condensed Structural Formulas

Condensed structural formulas are a simplified way of writing out the chemical structures of compounds. They allow chemists to clearly and concisely show the arrangement of atoms in a molecule without drawing out every single bond.

For instance, cyclohexene is represented as \(C_6H_{10}\), indicating six carbon atoms and ten hydrogen atoms arranged in a double-bonded ring. In the exercise, each reaction was expressed using these formulas to show balanced chemical equations, such as:

• \(C_5H_{10} + H_2O \rightarrow C_5H_{12}O + C_5H_{12}O\)

Condensed formulas help us focus on important functional groups and molecular transformations without getting lost in unnecessary details. This method is especially beneficial when communicating complex reaction mechanisms and structural data in organic chemistry.