Savin Writing Reaction Mechanisms in Organic Chemistry

3. Auflage 2014
ISBN: 978-0-12-410509-6
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 510 Seiten

Writing Reaction Mechanisms in Organic Chemistry, Third Edition, is a guide to understanding the movements of atoms and electrons in the reactions of organic molecules. Expanding on the successful book by Miller and Solomon, this new edition further enhances your understanding of reaction mechanisms in organic chemistry and shows that writing mechanisms is a practical method of applying knowledge of previously encountered reactions and reaction conditions to new reactions. The book has been extensively revised with new material including a completely new chapter on oxidation and reduction reactions including stereochemical reactions. It is also now illustrated with hundreds of colorful chemical structures to help you understand reaction processes more easily. The book also features new and extended problem sets and answers to help you understand the general principles and how to apply these to real applications. In addition, there are new information boxes throughout the text to provide useful background to reactions and the people behind the discovery of a reaction. This new edition will be of interest to students and research chemists who want to learn how to organize what may seem an overwhelming quantity of information into a set of simple general principles and guidelines for determining and describing organic reaction mechanisms. - Extensively rewritten and reorganized with a completely new chapter on oxidation and reduction reactions including stereochemical reactions - Essential for those who need to have mechanisms explained in greater detail than most organic chemistry textbooks provide - Now illustrated with hundreds of colorful chemical structures to help you understand reaction processes more easily - New and extended problem sets and answers to help you understand the general principles and how to apply this to real applications - New information boxes throughout the text to provide useful background to reactions and the people behind the discovery of a reaction

Autoren/Hrsg.

Savin, Kenneth A.

Inhaltsverzeichnis

1;Front Cover;1
2;Writing Reaction Mechanisms in Organic Chemistry;4
3;Copyright;5
4;Contents;6
5;Acknowledgments for the Third Edition;8
6;Chapter 1 - Introduction—Molecular Structure and Reactivity;10
6.1;1 HOW TO WRITE LEWIS STRUCTURES AND CALCULATE FORMAL CHARGES;10
6.2;2 REPRESENTATIONS OF ORGANIC COMPOUNDS;20
6.3;3 GEOMETRY AND HYBRIDIZATION;21
6.4;4 ELECTRONEGATIVITIES AND DIPOLES;23
6.5;5 RESONANCE STRUCTURES;25
6.6;6 AROMATICITY AND ANTIAROMATICITY;31
6.7;7 TAUTOMERS AND EQUILIBRIUM;34
6.8;8 ACIDITY AND BASICITY;37
6.9;9 NUCLEOPHILES AND ELECTROPHILES;41
6.10;ANSWERS TO PROBLEMS;45
6.11;References;62
7;Chapter 2 - General Principles for Writing Reaction Mechanisms;64
7.1;1 BALANCING EQUATIONS;65
7.2;2 USING ARROWS TO SHOW MOVING ELECTRONS;67
7.3;3 MECHANISMS IN ACIDIC AND BASIC MEDIA;70
7.4;4 ELECTRON-RICH SPECIES: BASES OR NUCLEOPHILES?;76
7.5;5 TRIMOLECULAR STEPS;78
7.6;6 STABILITY OF INTERMEDIATES;79
7.7;7 DRIVING FORCES FOR REACTIONS;82
7.8;8. STRUCTURAL RELATIONSHIPS BETWEEN STARTING MATERIALS AND PRODUCTS;84
7.9;9 SOLVENT EFFECTS;86
7.10;10 A LAST WORD;87
7.11;ANSWERS TO PROBLEMS;90
7.12;References;101
8;Chapter 3 - Reactions of Nucleophiles and Bases;102
8.1;1 NUCLEOPHILIC SUBSTITUTION;103
8.2;2 ELIMINATIONS AT SATURATED CARBON;114
8.3;3 NUCLEOPHILIC ADDITION TO CARBONYL COMPOUNDS;116
8.4;4 BASE-PROMOTED REARRANGEMENTS;130
8.5;5 ADDITIONAL MECHANISMS IN BASIC MEDIA;132
8.6;ANSWERS TO PROBLEMS;138
8.7;References;167
9;Chapter 4 - Reactions Involving Acids and Other Electrophiles;170
9.1;1 STABILITY OF CARBOCATIONS;170
9.2;2 FORMATION OF CARBOCATIONS;171
9.3;3 THE FATE OF CARBOCATIONS;173
9.4;4 REARRANGEMENT OF CARBOCATIONS;174
9.5;5 ELECTROPHILIC ADDITION;181
9.6;6 ACID-CATALYZED REACTIONS OF CARBONYL COMPOUNDS;185
9.7;7 ELECTROPHILIC AROMATIC SUBSTITUTION;191
9.8;8 CARBENES;195
9.9;9 ELECTROPHILIC HETEROATOMS;202
9.10;ANSWERS TO PROBLEMS;209
9.11;References;243
10;Chapter 5 - Radicals and Radical Anions;246
10.1;I INTRODUCTION;246
10.2;2 FORMATION OF RADICALS;246
10.3;3 RADICAL CHAIN PROCESSES;249
10.4;4 RADICAL INHIBITORS;252
10.5;5 DETERMINING THE THERMODYNAMIC FEASIBILITY OF RADICAL REACTIONS;253
10.6;6 ADDITION OF RADICALS;256
10.7;7 FRAGMENTATION REACTIONS;261
10.8;8 REARRANGEMENT OF RADICALS;265
10.9;9 THE SRN1 REACTION;268
10.10;10 THE BIRCH REDUCTION;271
10.11;11 A RADICAL MECHANISM FOR THE REARRANGEMENT OF SOME ANIONS;273
10.12;ANSWERS TO PROBLEMS;277
10.13;References;300
11;Chapter 6 - Pericyclic Reactions;302
11.1;1 INTRODUCTION;302
11.2;2 ELECTROCYCLIC REACTIONS;304
11.3;3 CYCLOADDITIONS;311
11.4;4 SIGMATROPIC REARRANGEMENTS;321
11.5;5 THE ENE REACTION;328
11.6;6 A MOLECULAR ORBITAL VIEW OF PERICYCLIC PROCESSES;332
11.7;ANSWERS TO PROBLEMS;346
11.8;References;361
12;Chapter 7 - Oxidations and Reductions;364
12.1;1 DEFINITION OF OXIDATION AND REDUCTION;364
12.2;2 OXIDATIONS;369
12.3;3 REDUCTIONS;394
12.4;ANSWERS TO PROBLEMS;425
12.5;References;438
13;Chapter 8 - Additional Problems;442
13.1;ANSWERS TO PROBLEMS;451
13.2;References;489
14;Appendix A - Lewis Structures of Common Functional Groups;490
15;Appendix B - Symbols and Abbreviations Used in Chemical Notation;492
16;Appendix C - Relative Acidities of Common Organic and Inorganic Substancesa;494
17;Index;502

Leseproben

Chapter 1 Introduction—Molecular Structure and Reactivity
Abstract
To understand the way atoms bond to one another and then transform into new structures it is important to have a common set of rules and definitions. Herein, we describe key aspects of bonding, equilibrium, and driving forces that influence the structure and allow us to model and predict what are otherwise very complicated events. Many of the concepts presented in this chapter are a review for the student who has already taken the basic Organic series and the General Chemistry sequence, with a few new concepts and further explanations on some specific topics. This chapter helps create a common language and concepts that will be encountered in the book. Keywords
Acidity; Aromaticity; Basicity; Bond; Charge; Dipole; Electronegativity; Electrophile; Formal charge; Hybridization; Lewis structure; Nucleophile; Octet; Resonance; Tautomers Reaction mechanisms offer us insights into how molecules react, enable us to manipulate the course of known reactions, aid us in predicting the course of known reactions using new substrates, and help us to develop new reactions and reagents. In order to understand and write reaction mechanisms, it is essential to have a detailed knowledge of the structures of the molecules involved and to be able to notate these structures unambiguously. In this chapter, we present a review of the fundamental principles relating to molecular structure and of the ways to convey structural information. A crucial aspect of structure from the mechanistic viewpoint is the distribution of electrons, so this chapter outlines how to analyze and depict electron distributions. Mastering the material in this chapter will provide you with the tools you need to propose reasonable mechanisms and to convey these mechanisms clearly to others. 1. How to Write Lewis Structures and Calculate Formal Charges
The ability to construct Lewis structures is fundamental to writing or understanding organic reaction mechanisms. It is particularly important because lone pairs of electrons frequently are crucial to the mechanism but often are omitted from structures appearing in the chemical literature. There are two methods commonly used to show Lewis structures. One shows all electrons as dots. The other shows all bonds (two shared electrons) as lines and all unshared electrons as dots. A. Determining the Number of Bonds
HINT 1.1 To facilitate the drawing of Lewis structures, estimate the number of bonds. For a stable structure with an even number of electrons, the number of bonds is given by the equation: ElectronDemand?ElectronSupply)/2=NumberofBonds   The electron demand is two for hydrogen and eight for all other atoms usually considered in organic chemistry. (The tendency of most atoms to acquire eight valence electrons is known as the octet rule.) For elements in group IIIA (e.g., B, Al, Ga), the electron demand is six. Other exceptions are noted, as they arise, in examples and problems. For neutral molecules, the contribution of each atom to the electron supply is the number of valence electrons of the neutral atom. (This is the same as the group number of the element when the periodic table is divided into eight groups.) For ions, the electron supply is decreased by one for each positive charge of a cation and is increased by one for each negative charge of an anion. Use the estimated number of bonds to draw the number of two-electron bonds in your structure. This may involve drawing a number of double and triple bonds (see the following section). B. Determining the Number of Rings and/or ? Bonds (Degree of Unsaturation)
The total number of rings and/or ? bonds can be calculated from the molecular formula, bearing in mind that in an acyclic saturated hydrocarbon the number of hydrogens is 2n + 2, where n is the number of carbon atoms. Each time a ring or ? bond is formed, there will be two fewer hydrogens needed to complete the structure. HINT 1.2 On the basis of the molecular formula, the degree of unsaturation for a hydrocarbon is calculated as (2m + 2 ? n)/2, where m is the number of carbons and n is the number of hydrogens. The number calculated is the number of rings and/or ? bonds. For molecules containing heteroatoms, the degree of unsaturation can be calculated as follows: Nitrogen: For each nitrogen atom, subtract 1 from n. Halogens: For each halogen atom, add 1 to n. Oxygen: Use the formula for hydrocarbons. This method cannot be used for molecules in which there are atoms like sulfur and phosphorus whose valence shell can expand beyond eight. EXAMPLE 1.1 CALCULATE THE NUMBER OF RINGS AND/OR ? BONDS CORRESPONDING TO EACH OF THE FOLLOWING MOLECULAR FORMULAS a. C2H2Cl2Br2 There are a total of four halogen atoms. Using the formula (2m + 2 ? n)/2, we calculate the degree of unsaturation to be (2(2) + 2 ? (2 + 4))/2 = 0. b. C2H3N There is one nitrogen atom, so the degree of unsaturation is (2(2) + 2 ? (3?1)) = 2. C. Drawing the Lewis Structure
Start by drawing the skeleton of the molecule, using the correct number of rings or ? bonds, and then attach hydrogen atoms to satisfy the remaining valences. For organic molecules, the carbon skeleton frequently is given in an abbreviated form. Once the atoms and bonds have been placed, add lone pairs of electrons to give each atom a total of eight valence electrons. When this process is complete, there should be two electrons for hydrogen; six for B, Al, or Ga; and eight for all other atoms. The total number of valence electrons for each element in the final representation of a molecule is obtained by counting each electron around the element as one electron, even if the electron is shared with another atom. (This should not be confused with counting electrons for charges or formal charges; see Section 1.D.) The number of valence electrons around each atom equals the electron demand. Thus, when the number of valence electrons around each element equals the electron demand, the number of bonds will be as calculated in Hint 1.1. Atoms of higher atomic number can expand the valence shell to more than eight electrons. These atoms include sulfur, phosphorus, and the halogens (except fluorine). HINT 1.3 When drawing Lewis structures, make use of the following common structural features. 1. Hydrogen is always on the periphery because it forms only one covalent bond. 2. Carbon, nitrogen, and oxygen exhibit characteristic bonding patterns. In the examples that follow, the R groups may be hydrogen, alkyl, or aryl groups, or any combination of these. These substituents do not change the bonding pattern depicted. (a) Carbon in neutral molecules usually has four bonds. The four bonds may all be ? bonds, or they may be various combinations of ? and ? bonds (i.e., double and triple bonds).
    There are exceptions to the rule that carbon has four bonds. These include CO, isonitriles (RNC), and carbenes (neutral carbon species with six valence electrons; see Chapter 4). (b) Carbon with a single positive or negative charge has three bonds.
(c) Neutral nitrogen, with the exception of nitrenes (see Chapter 4), has three bonds and a lone pair.
(d) Positively charged nitrogen has four bonds and a positive charge; exceptions are nitrenium ions (see Chapter 4).
(e) Negatively charged nitrogen has two bonds and two lone pairs of electrons.
(f) Neutral oxygen has two bonds and two lone pairs of electrons.
(g) Oxygen–oxygen bonds are uncommon; they are present only in peroxides, hydroperoxides, and diacyl peroxides (see Chapter 5). The formula, RCO2R, implies the following structure:
(h) Positive oxygen usually has three bonds and a lone pair of electrons; exceptions are the very unstable oxenium ions, which contain a single bond to oxygen and two lone pairs of electrons.
3. Sometimes a phosphorus or sulfur atom in a molecule is depicted with 10...