Organic Chemistry Workbook

Theory, Reactivity and Mechanisms in Modern Synthesis

Pierre Vogel, Kendall N. Houk

• Publisher: Wiley-VCH
• Year: 2019
• ISBN:
  9783527819300
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Provides references and answers to every question presented in the primary Organic Chemistry textbook

Successfully achieving chemical reactions in organic chemistry requires a solid background in physical chemistry. Knowledge of chemical equilibria, thermodynamics, reaction rates, reaction mechanisms, and molecular orbital theory is essential for students, chemists, and chemical engineers. The Organic Chemistry presents the tools and models required to understand organic synthesis and enables the efficient planning of chemical reactions.

This volume, Organic Chemistry: Theory, Reactivity, and Mechanisms in Modern Synthesis Workbook, complements the primary textbook—supplying the complete, calculated solutions to more than 800 questions on topics such as thermochemistry, pericyclic reactions, organic photochemistry, catalytic reactions, and more. This companion workbook is indispensable for those seeking clear, in-depth instruction on this challenging subject.

Written by prominent experts in the field of organic chemistry, this book:

• Works side-by-side with the primary Organic Chemistry textbook
• Includes chapter introductions and re-stated questions to enhance efficiency
• Features clear illustrations, tables, and figures
• Strengthens reader?s comprehension of key areas of knowledge

Organic Chemistry: Theory, Reactivity, and Mechanisms in Modern Synthesis Workbook is a must-have resource for anyone using the primary textbook.

1
Equilibria and Thermochemistry

Answers to Problems

Problem 1.1

A hydrocarbon, RH, can be isomerized in reversible reactions into two isomeric compounds P1 and P2 with the same heat of reaction. Both have C₁ symmetry. P1 is a rigid molecule, and P2 is a flexible one adopting several conformations of similar stability. Which product will be preferred at equilibrium?

Answer

Products P1 and P2 equilibrate with RH in reversible reactions at temperature T. The preferred product will be that for which the free energy of reaction Δ_rG^T(reactants ⇆ product P1 or P2) = Δ_rH^T − TΔ_rS^T is the smallest. If Δ_rH^T(RH ⇆ P1) = Δ_rH^T(RH ⇆ P2), the product with the largest entropy (S^T(P1), S^T(P2)), will be favored at equilibrium at temperature T. Entropy expresses the degree of freedom available to an ensemble of molecules of a given compound. It depends upon the number of different microscopic states available to these molecules, and this depends on the size of the molecules themselves (P1 and P2 have the same molecular weight as they are isomers of the starting material RH), and the energy separation between the microscopic states available to them. The microscopic states that contribute most to the entropy are translational and rotational states for which the energy separation between quantum levels are the smallest. A rigid molecule is a molecule that does not equilibrate with several conformers of similar stabilities. It has only one energy minimum along all the coordinates that describe its geometrical deformations, including torsion about its σ‐ and π‐bonds and bond elongation. A flexible molecule evolves at temperature T among several energy minima. In other words, several energy minima are populated significantly at the given temperature T. This is the case for P2, not for P1. If those energy minima correspond to different geometries (no rotation symmetry axis, σ = 1) the flexible molecule has a larger entropy than the rigid molecule; thus S^T(P2) > S^T(P1), and Δ_rG^T(RH ⇆ P2) < Δ_rG^T(RH ⇆ P1). Product P2 that is composed of flexible molecules will be formed to a larger extent than product P1 composed of rigid molecules at temperature T.

1. Problem 1.2
   Define the symmetry numbers, σ, of ethane, propane, cyclopropane, cyclobutane, cyclohexanone, ferrocene, bicyclo[2.2.1]hepta‐2,5‐diene (norbornadiene), 1,4‐difluorobenzene, meso‐tartaric acid, and (R,R)‐tartaric acid (see Figure 1.24 for the structure of the two latter compounds).
   Answer
2. Ethane is a flexible molecule that adopts a preferred staggered conformation (c. 3 kcal mol⁻¹ more stable than the eclipsed conformation (Section 2.5.1), transition state of the rotation about its σ(CC) bond). Ethane has a C₃‐ and three C₂‐axes that are interconverted by rotation about the C₃‐axis. Thus, the symmetry number σ = 3 × 2 = 6.

   

   Propane is a flexible molecule for which the doubly staggered conformation is the most stable one (C_2v symmetry: one mirror plane of symmetry containing a C₂‐axis of rotation) has one C₂‐axis of rotation. Thus, the symmetry number σ = 2.

   

   Cyclopropane is a rigid molecule (D_3h symmetry) with a C₃‐ and three C₂‐axes of rotation. Rotation about the C₃ axis interconverts the C₂‐axis. Thus, the symmetry numb...

Table of contents

• Cover
• Table of Contents
• 1 Equilibria and Thermochemistry
• 2 Additivity Rules for Thermodynamical Parameters and Deviations
• 3 The Rates of Chemical Reactions*
• 4 Molecular Orbital Theories
• 5 Pericyclic Reactions*
• 6 Organic Photochemistry
• 7 Catalytic Reactions
• 8 Transition‐Metal‐Catalyzed CC Bond Forming Reactions
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