Spectroscopic Methods in Organic Chemistry

Description

This book is the seventh edition of a well-established introductory guide to the interpretation of the mass, ultraviolet, infrared and nuclear magnetic resonance spectra of organic compounds. It is a textbook suitable for a course in the application of these techniques to structure determination and as a handbook for organic chemists to keep on their desks throughout their career. Preface Contents 1: Mass Spectra 1.1 Introduction 1.2 Ion Production 1.2.1 Electron Impact (EI) 1.2.2 Chemical Ionisation (CI) 1.2.3 Electrospray Ionisation (ESI) 1.2.4 Fast Ion Bombardment (FIB or LSIMS) 1.2.5 Laser Desorption (LD) and Matrix-Assisted Laser Desorption (MALDI) 1.3 Ion Analysis 1.3.1 Magnetic Analysers 1.3.2 Time-Of–Flight (TOF) Analysers 1.3.3 Quadrupole Analysers 1.3.4 Ion Cyclotron Resonance (ICR) Analysers 1.3.5 Ion-Trap Analysers 1.4 Structural Information from EI Mass Spectra 1.4.1 The Features of an EI Spectrum 1.4.2 The Molecular Ion 1.4.3 Isotopic Abundances 1.4.4 Identifying the Molecular Ion 1.4.5 Fragmentation in EI Spectra 1.5 Fragmentation in CI and FIB Spectra 1.5.1 Fragmentation in CI Spectra 1.5.2 Fragmentation in FIB (LSMIS) Spectra 1.6 Some Examples of Mass Spectrometry in Action 1.6.1 San Joaquin Oil 1.6.2 Oleic Acid 1.6.3 The Oviposition Pheromone 1.6.4 Identifying Antibodies 1.6.5 The ESI Spectra of Melittin and the Human Parathyroid Hormone 1.6.6 ESI-FT-ICR and ESI-FT-Orbitrap Spectra 1.7 Separation Coupled to Mass Spectrometry 1.7.1 GC/MS and LC/MS 1.7.2 MS/MS 1.8 Interpreting the Spectrum of an Unknown 1.9 Internet 1.10 Further Reading 1.11 Problems 1.12 Tables of Data References 2: Ultraviolet and Visible Spectra 2.1 Introduction 2.2 Chromophores 2.3 The Absorption Laws 2.4 Measurement of the Spectrum 2.5 Vibrational Fine Structure 2.6 Selection Rules and Intensity 2.7 Solvent Effects 2.8 Searching for a Chromophore 2.9 Definitions 2.10 Conjugated Dienes 2.11 Polyenes and Poly-Ynes 2.12 Ketones and Aldehydes; π→π∗ Transitions 2.13 Ketones and Aldehydes; n→π∗ Transitions 2.14 α,β-Unsaturated Acids, Esters, Nitriles and Amides 2.15 Aromatic Compounds 2.16 Quinones 2.17 Corroles, Chlorins and Porphyrins 2.18 Non-conjugated Interacting Chromophores 2.19 The Effect of Steric Hindrance to Coplanarity 2.20 Internet 2.21 Further Readings 2.22 Problems References 3: Infrared and Raman Spectra 3.1 Introduction 3.2 Preparation of Samples and Examination in an Infrared Spectrometer 3.3 Selection Rules 3.4 The Infrared Spectrum 3.5 The Use of the Tables of Characteristic Group Frequencies 3.6 Stretching Frequencies of Single Bonds to Hydrogen 3.7 Stretching Frequencies of Triple and Cumulated Double Bonds 3.8 Stretching Frequencies in the Double-Bond Region 3.9 Characteristic Vibrations of Aromatic Rings 3.10 Groups Absorbing in the Fingerprint Region 3.11 Raman Spectra 3.12 Internet 3.13 Further Reading 3.14 Problems 3.15 Correlation Charts 3.16 Tables of Data 4: 1D Nuclear Magnetic Resonance Spectra 4.1 Nuclear Spin and Resonance 4.2 Taking a Spectrum 4.3 The Chemical Shift 4.4 Factors Affecting the Chemical Shift 4.4.1 The Inductive Effect 4.4.2 Anisotropy of Chemical Bonds 4.4.3 Polar Effects of Conjugation 4.4.4 Van der Waals Forces 4.4.5 Isotope Effects 4.4.6 Estimating a Chemical Shift 4.4.7 Hydrogen Bonds 4.4.8 Solvent Effects and Temperature 4.5 Spin-Spin Coupling to 13C 4.5.1 13C–2H Coupling 4.5.2 13C–1H Coupling 4.5.3 13C–13C Coupling 4.6 1H–1H Coupling: Multiplicity and Coupling Patterns 4.6.1 1H–1H Vicinal Coupling (3JHH) 4.6.2 AB Systems 4.6.3 1H–1H Geminal Coupling (2JHH) 4.6.4 1H–1H Long-Range Coupling (4JHH and 5JHH) 4.6.5 Deviations From First-Order Coupling 4.7 1H–1H Coupling: The Magnitude of Coupling Constants 4.7.1 The Sign of Coupling Constants 4.7.2 Vicinal Coupling (3JHH) 4.7.3 Geminal Coupling (2JHH) 4.7.4 Long-Range Coupling (4JHH and 5JHH) 4.7.5 C–H Coupling (1JCH, 2JCH and 3JCH) 4.8 Coupling From 1H and 13C to 19F and 31P 4.8.1 13C NMR Spectra of Compounds Containing 19F and 31P 4.8.2 1H NMR Spectra of Compounds Containing 19F and 31P 4.9 Relaxation and Its Consequences 4.9.1 Longitudinal Relaxation 4.9.2 Transverse Relaxation and Exchange 4.10 Improving the NMR Spectrum 4.10.1 The Effect of Changing the Magnetic Field 4.10.2 Solvent Effects 4.10.3 Shift Reagents 4.11 Spin Decoupling 4.11.1 Simple Spin Decoupling 4.11.2 Difference Decoupling 4.12 Identifying Spin Systems: 1D-TOCSY 4.13 The Nuclear Overhauser Effect 4.13.1 Origins 4.13.2 NOE-Difference Spectra 4.14 The Rotating Frame of Reference 4.15 Assignment of CH3, CH2, CH and Fully Substituted Carbons in 13C NMR 4.15.1 The Attached Proton Test (APT) 4.15.2 DEPT 4.16 Hints for Structure Determination Using 1D-NMR 4.16.1 Carbon Spectra 4.16.2 Proton Spectra 4.17 Further Information 4.17.1 The Internet 4.17.2 Further Reading 4.18 Tables of Data References 5: 2D-Nuclear Magnetic Resonance Spectra 5.1 The Basic Pulse Sequence 5.2 COSY 5.2.1 Cross Peaks from Scalar Coupling 5.2.2 Polarisation Transfer 5.2.3 The Origin of Cross Peaks 5.2.4 Displaying COSY Spectra 5.2.5 Interpreting COSY Spectra 5.2.6 Axial Signals 5.2.7 Gradient Pulses 5.2.8 DQF-COSY 5.2.9 Phase Structure in COSY Spectra 5.3 2D-TOCSY 5.4 NOESY 5.5 Cross-Correlated 2D Spectra Identifying 1-Bond Connections 5.5.1 Heteronuclear Multiple Quantum Coherence (HMQC) Spectra 5.5.2 Heteronuclear Single Quantum Coherence (HSQC) Spectra 5.5.3 Examples of HSQC Spectra 5.5.4 Non-Uniform Sampling (NUS) 5.5.5 Cross-Peak Detail: Determining the Sign of Coupling Constants 5.5.6 Clip-HSQC 5.5.7 Deconvoluting a 1H-Spectrum Using the HSQC Spectrum 5.5.8 HSQC-TOCSY 5.5.9 HETCOR 5.6 Cross-Correlated 2D Spectra Identifying 2- and 3-Bond Connections 5.6.1 The HMBC Pulse Sequence 5.6.2 HMBC Spectra 5.7 Some Specialised NMR Techniques 5.7.1 ADEQUATE: Identifying 13C–13C Connections 5.7.2 INADEQUATE: Identifying 13C–13C Connections 5.7.3 HSQC-HECADE: Measuring the Sign and Magnitude of 13C–1H Coupling Constants 5.8 Three- and Four-Dimensional NMR 5.9 Hints for Structure Determination Using 2D-NMR 5.10 Further Reading 5.11 Table of Information Reference 6: Worked Examples 6.1 General Approach 6.2 Simple Worked Examples Using 13C NMR Alone 6.3 Simple Worked Examples Using 1H NMR Alone 6.4 Simple Worked Examples Using the Combined Application of MS, UV, IR and 1D-NMR Spectroscopic Methods 6.5 Worked Examples Using the Combined Application of MS, UV, IR, 1D-NMR and 2D-NMR Spectroscopic Methods 7: Problem Sets 7.1 Chemical Shift Problems 7.2 1D-NMR Chemical Shift and Coupling Problems 7.3 Problems Using all the Spectroscopic Methods Index