Organic Structures from Spectra

The derivation of structural information from spectroscopic data is now an integral part of organic chemistry courses at all Universities. A critical part of any such course is a suitable set of problems to develop the students’ understanding of how organic structures are determined from spectra. The book builds on the very successful teaching philosophy of learning by hands-on problem solving; carefully graded examples build confidence and develop and consolidate a student’s understanding of organic spectroscopy. Organic Structures from Spectra, 6th Edition is a carefully chosen set of about 250 structural problems employing the major modern spectroscopic techniques, including Mass Spectrometry, 1D and 2D 13C and 1H NMR Spectroscopy and Infrared Spectroscopy. There are 25 problems specifically dealing with the interpretation of spin–spin coupling in proton NMR spectra and 10 problems based on the quantitative analysis of mixtures using proton and carbon NMR spectroscopy. The accompanying text is descriptive and only explains the underlying theory at a level that is sufficient to tackle the problems. The text includes condensed tables of characteristic spectral properties covering the frequently encountered functional groups. The examples themselves have been selected to include all important structural features and to emphasise connectivity arguments and stereochemistry. Many of the compounds were synthesised specifically for this book. In this collection, there are many additional easy problems designed to build confidence and to demonstrate basic principles. The Sixth Edition of this popular textbook: now incorporates many new problems using 2D NMR spectra (C–H Correlation spectroscopy, HMBC, COSY, NOESY and TOCSY); has been expanded and updated to reflect the new developments in NMR spectroscopy; has an additional 40 carefully selected basic problems; provides a set of problems dealing specifically with the quantitative analysis of mixtures using NMR spectroscopy; features proton NMR spectra obtained at 200, 400 and 600 MHz and 13C NMR spectra including routine 2D C–H correlation, HMBC spectra and DEPT spectra; contains a selection of problems in the style of the experimental section of a research paper; includes examples of fully worked solutions in the appendix; has a complete set of solutions available to instructors and teachers from the authors. Organic Structures from Spectra, Sixth Edition will prove invaluable for students of Chemistry, Pharmacy and Biochemistry taking a first course in Organic Chemistry.

Table of Contents:
Preface ix List of Tables xiii List of Figures xv 1 Introduction 1 1.1 General Principles of Absorption Spectroscopy 1 1.2 Chromophores 2 1.3 Degree of Unsaturation 3 1.4 Connectivity 4 1.5 Sensitivity 4 1.6 Practical Considerations 5 2 Ultraviolet (UV) Spectroscopy 6 2.1 The Nature of Ultraviolet Spectroscopy 6 2.2 Basic Instrumentation 6 2.3 Quantitative Aspects of Ultraviolet Spectroscopy 8 2.4 Classification of UV Absorption Bands 8 2.5 Special Terms in Ultraviolet Spectroscopy 9 2.6 Important UV Chromophores 10 2.6.1 Dienes and Polyenes 10 2.6.2 Carbonyl Compounds 11 2.6.3 Benzene Derivatives 11 2.7 The Effect of Solvents 13 3 Infrared (IR) Spectroscopy 14 3.1 Absorption Range and the Nature of IR Absorption 14 3.2 Experimental Aspects of Infrared Spectroscopy 15 3.3 General Features of Infrared Spectra 16 3.4 Important IR Chromophores 18 3.4.1 –O–H and –N–H Stretching Vibrations 18 3.4.2 C–H Stretching Vibrations 18 3.4.3 –C≡N and –C≡C– Stretching Vibrations 19 3.4.4 Carbonyl Groups 19 3.4.5 Other Polar Functional Groups 21 3.4.6 The Fingerprint Region 21 4 Mass Spectrometry 23 4.1 Ionisation Processes 23 4.2 Instrumentation 25 4.3 Mass Spectral Data 26 4.3.1 High Resolution Mass Spectra 26 4.3.2 Molecular Fragmentation 28 4.3.3 Isotope Ratios 29 4.3.4 Chromatography Coupled With Mass Spectrometry 31 4.3.5 Metastable Peaks 31 4.4 Representation of Fragmentation Processes 31 4.5 Factors Governing Fragmentation Processes 32 4.6 Examples of Common Types of Fragmentation 32 4.6.1 Cleavage at Branch Points 32 4.6.2 Β-Cleavage 33 4.6.3 Cleavage Α to Carbonyl Groups 33 4.6.4 Cleavage Α to Heteroatoms 34 4.6.5 Retro Diels–Alder Reaction 34 4.6.6 The Mclafferty Rearrangement 34 5 1H Nuclear Magnetic Resonance (NMR) Spectroscopy 36 5.1 The Physics of Nuclear Spins and NMR Instruments 36 5.1.1 The Larmor Equation and Nuclear Magnetic Resonance 36 5.2 Basic NMR Instrumentation 39 5.2.1 CW and Pulsed NMR Spectrometers 39 5.2.2 Nuclear Relaxation 42 5.2.3 Magnets for NMR Spectroscopy 43 5.2.4 The NMR Spectrum 44 5.3 Chemical Shift in 1H NMR Spectroscopy 45 5.4 Spin–Spin Coupling in 1H NMR Spectroscopy 52 5.4.1 Signal Multiplicity – The N+1 Rule 54 5.5 Analysis of 1H NMR Spectra 55 5.5.1 Spin Systems 56 5.5.2 Strongly and Weakly Coupled Spin Systems 56 5.5.3 Magnetic Equivalence 58 5.5.4 Conventions for Naming Spin Systems 59 5.5.5 Spectral Analysis of First-Order NMR Spectra 60 5.5.6 Splitting Diagrams 61 5.5.7 Spin Decoupling 64 5.6 Correlation of 1H–1H Coupling With Structure 65 5.6.1 Non-Aromatic Spin Systems 65 5.6.2 Aromatic Spin Systems 66 5.7 The Nuclear Overhauser Effect (NOE) 69 5.8 Labile and Exchangeable Protons 70 6 13c NMR Spectroscopy 72 6.1 Coupling and Decoupling in 13c NMR Spectra 72 6.2 The Nuclear Overhauser Effect (NOE) in 13c NMR Spectroscopy 73 6.3 Determining 13c Signal Multiplicity Using Dept 73 6.4 Shielding and Characteristic Chemical Shifts in 13c NMR Spectra 76 7 2-Dimensional NMR Spectroscopy 82 7.1 Proton–Proton Interactions By 2D NMR 85 7.1.1 COSY (Correlation Spectroscopy) 85 7.1.2 TOCSY (Total Correlation Spectroscopy) 86 7.1.3 NOESY (Nuclear Overhauser Effect Spectroscopy) 88 7.2 Proton–Carbon Interactions By 2D NMR 89 7.2.1 The HSQC (Heteronuclear Single Quantum Correlation) or HSC (Heteronuclear Shift Correlation) Spectrum 89 7.2.2 HMBC (Heteronuclear Multiple Bond Correlation) 91 8 Miscellaneous Topics 96 8.1 Solvents for NMR Spectroscopy 96 8.2 Solvent-Induced Shifts 97 8.3 Dynamic Processes in NMR – The NMR Time-Scale 98 8.3.1 Conformational Exchange Processes 99 8.3.2 Intermolecular Exchange of Labile Protons 99 8.3.3 Rotation About Partial Double Bonds 100 8.4 The Effect of Chirality 100 8.5 The NMR Spectra of “Other Nuclei” 101 9 Determining the Structure of Organic Compounds From Spectra 102 9.1 Solving Problems 103 9.2 Worked Examples 104 10 Problems 115 Index 538

About the Author :
L. D. Field, Professor of Chemistry, School of Chemistry, University of New South Wales, Australia H. L. Li, Senior Research Associate, School of Chemistry, University of New South Wales, Australia A. M. Magill, Honorary Associate, School of Chemistry, University of New South Wales, Australia