Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 116

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Chapter 3, Problem 116

One of the most bizarre reactions in chemistry is called the Ugi reaction: R1C(=O)R2 + R3 - NH2 + R4COOH + R5NC S R4C(=O)N(R3)C(R1R2)C=ONHR5 + H2O
(a) Write out the balanced chemical equation for the Ugi reaction, for the case where R = CH3CH2CH2CH2CH2CH2— (this is called the hexyl group) for all compounds.

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Identify the reactants and products in the Ugi reaction: R1C(=O)R2, R3-NH2, R4COOH, and R5NC.

Substitute the hexyl group (CH3CH2CH2CH2CH2CH2—) for each R group in the reaction.

Write the chemical formula for each reactant with the hexyl group: CH3CH2CH2CH2CH2CH2C(=O)CH3, CH3CH2CH2CH2CH2CH2-NH2, CH3CH2CH2CH2CH2CH2COOH, and CH3CH2CH2CH2CH2CH2NC.

Combine the reactants to form the product: CH3CH2CH2CH2CH2CH2C(=O)N(CH3CH2CH2CH2CH2CH2)C(CH3CH2CH2CH2CH2CH2CH3)C=ONHCH3CH2CH2CH2CH2CH2 + H2O.

Ensure the chemical equation is balanced by checking that the number of atoms of each element is the same on both sides of the equation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ugi Reaction

The Ugi reaction is a multicomponent reaction that combines an isocyanide, an aldehyde or ketone, an amine, and a carboxylic acid to form a β-amino acid. This reaction is notable for its ability to create complex molecules from simple starting materials in a single step, making it valuable in organic synthesis and medicinal chemistry.

Balanced Chemical Equation

A balanced chemical equation represents a chemical reaction with equal numbers of each type of atom on both sides of the equation. Balancing ensures the law of conservation of mass is upheld, meaning that matter is neither created nor destroyed during the reaction. This is crucial for accurately predicting the amounts of reactants and products involved.

Hexyl Group

The hexyl group is a hydrocarbon chain consisting of six carbon atoms (C6H13) and is derived from hexane. In the context of the Ugi reaction, substituting the hexyl group into the reactants allows for the exploration of how different alkyl chains affect the reaction's outcome and the properties of the resulting compounds.

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The Alkyl Groups Example

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Textbook Question

The source of oxygen that drives the internal combustion engine in an automobile is air. Air is a mixture of gases, principally N₂(79%) and O₂(20%). In the cylinder of an automobile engine, nitrogen can react with oxygen to produce nitric oxide gas, NO. As NO is emitted from the tailpipe of the car, it can react with more oxygen to produce nitrogen dioxide gas. (c) The production of NOx gases is an unwanted side reaction of the main engine combustion process that turns octane, C₈H₁₈, into CO₂ and water. If 85% of the oxygen in an engine is used to combust octane and the remainder used to produce nitrogen dioxide, calculate how many grams of nitrogen dioxide would be produced during the combustion of 500 g of octane.

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Textbook Question

The thermite reaction, Fe₂O₃ + Al → Al₂O₃ + Fe produces so much heat that the Fe product melts. This reaction is used industrially to weld metal parts under water, where a torch cannot be employed. It is also a favorite chemical demonstration in the lecture hall (on a small scale). (b) Calculate how many grams of aluminum are needed to completely react with 500.0 g of Fe₂O₃ in this reaction.

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Textbook Question

The thermite reaction, Fe2O3 + Al S Al2O3 + Fe produces so much heat that the Fe product melts. This reaction is used industrially to weld metal parts under water, where a torch cannot be employed. It is also a favorite chemical demonstration in the lecture hall (on a small scale). (d) If you performed the reverse reaction— aluminum oxide plus iron makes iron oxide plus aluminum—would that reaction have heat as a reactant or a product?

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