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Chapter 35: Problem 797

Irradiation of benzophenone in isopropyl alcohol in the presence of oxygen gives no benzopinacol (the benzophenone is not consumed), acetone (with \(\Phi\) equal to unity), and hydrogen peroxide (with \(\Phi\) nearly unity). The reaction does not occur readily in the absence of benzophenone. Explain how benzophenone aces as a photosensitizer for the oxidation of isopropyl alcohol by oxygen.

Short Answer

Expert verified
Benzophenone acts as a photosensitizer for the oxidation of isopropyl alcohol by oxygen. Upon irradiation, excited benzophenone transfers its energy to other molecules, forming intermediate species with oxygen and isopropyl alcohol. These intermediates then react, producing acetone and hydrogen peroxide without consuming benzophenone. The reaction can only occur in the presence of oxygen, as it contributes to the formation of intermediate species and determines the final products.

Step by step solution

01

Understand the Benzophenone and Isopropyl Alcohol System

Benzophenone is a molecule that, when exposed to light, can get excited to a higher energy state. In the presence of isopropyl alcohol, photoexcited benzophenone can transfer its energy, leading to a chemical reaction. In the presence of oxygen, the reaction does not produce benzopinacol, but it does create acetone and hydrogen peroxide. However, the reaction is not observed in the absence of benzophenone, indicating that it has a crucial role in the process.
02

Photosensitizer Concept

A photosensitizer is a molecule that can absorb light and transfer its energy to other molecules, initiating a chemical reaction. The photosensitizer does not get consumed in the process and can carry on the cycle, starting from its ground state. In this case, benzophenone acts as a photosensitizer.
03

Analyze the Reaction Mechanism

When benzophenone is irradiated, it gets excited to a higher energy state. Since it can effectively absorb the energy required for the reaction, it transfers its energy to other molecules, such as to form a reactive intermediate species between oxygen and the isopropyl alcohol. The intermediate species then go on to react further, producing acetone and hydrogen peroxide, ultimately consuming the isopropyl alcohol. As benzophenone does not get consumed during this process, it acts as a photosensitizer for the reaction.
04

Role of Oxygen

Oxygen is an essential component in the reaction and contributes to the formation of intermediate species. During the energy transfer process, oxygen molecules react with excited isopropyl alcohol radicals to form the products of acetone and hydrogen peroxide. The presence of oxygen affects the overall reaction mechanism and determines the formed products.
05

Conclusion

To sum up, benzophenone acts as a photosensitizer in the oxidation of isopropyl alcohol with oxygen. When benzophenone is irradiated, it gets excited to a higher energy state and transfers its energy to other molecules, forming intermediate species with oxygen and isopropyl alcohol. These intermediates further react to produce acetone and hydrogen peroxide without consuming benzophenone in the process, explaining why the reaction does not occur readily without benzophenone. The role of oxygen is essential to drive the reaction mechanism and determine the final products formed.

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Most popular questions from this chapter

Explain qualitatively how temperature could have an effect on the appearance of the absorption spectrum of a system such as that shown, knowing that most molecules are usually in their lowest vibrational state at room temperature. Schematic potential energy diagram for ground and excited electronic singlet states of a diatomic molecule, \(\mathrm{A}-\mathrm{B}\) and \(\mathrm{A}-\mathrm{B}^{*}\), respectively. The horizontal lines represent vibrational energy levels. The wavy lines represent the arrival or departure of light quanta. It is important to recognize that the curves shown here are schematic and, for actual systems, the positions and shapes of the curves may be quite different from those shown.

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