Organic Spectroscopy

Transcription

1 Organic Spectroscopy William Kemp Senior Lecturer in Organic Chemistry Heriot-Watt University, Edinburgh THIRD EDITION M MACMILLAN

2 Contents Preface to the First Edition xiv Preface to the Second Edition xvi Preface to the Third Edition xviii Acknowledgments xxi 1 Energy and the Electromagnetic Spectrum Units,2 1.2 The Electromagnetic Spectrum Absorption of Electromagnetic Radiation by Organic Molecules 7 Supplement Spectroscopy and Computers Fourier Transforms Frequency and Time Spectroscopy and Chromatography Hyphenated Techniques Gas chromatography and spectroscopy Liquid chromatography and spectroscopy 15 Further reading 16 2 Infrared Spectroscopy Units of Frequency, Wavelength and Wavenumber Molecular Vibrations Calculation of vibrational frequencies 26

3 VI Modes of vibration Quantum restrictions 28 CONTENTS 2.3 Factors Influencing Vibrational Frequencies Vibrational coupling Hydrogen bonding Electronic effects Bond angles Field effects Instrumentation the Infrared Spectrometer Dispersive and Interferometric Instruments Infrared sources Monochromators Detectors Mode of operation dispersive instruments optical null and ratio recording Mode of operation interferometric instruments Fourier Transform infrared spectroscopy Calibration of the frequency scale Absorbance and transmittance scales Sampling Techniques Gases Liquids Solids Solutions Applications of Infrared Spectroscopy Identity by Fingerprinting Applications of Infrared Spectroscopy Identification of Functional Groups 56 Correlation Charts The Carbon Skeleton (Chart 1) Aromatics (Chart l(i)) Alkanes and alkyl groups (Chart l(ii)) Alkenes (Chart l(iii)) Alkynes (Chart l(iv)) Carbonyl Compounds (Chart 2) Aldehydes and ketones (including quinones) Chart 2(i)) Esters and lactones (Chart 2(ii)) Carboxylic acids and their salts (Chart 2(iii)) Amino acids (Chart 2(iv)) Carboxylic acid anhydrides (Chart 2(v)) 78

4 CONTENTS Amides (primary and N-substituted) (Chart 2(vi)) Acyl halides (Chart 2(vii)) Hydroxy Compounds and Ethers (Chart 3) Alcohols (Chart 3(i)) Carbohydrates (Chart 3(ii)) Phenols (Chart 3(iii)) Ethers (Chart 3(iv)) Nitrogen Compounds (Chart 4) Amines (Chart 4(i)) Imines and aldehyde-ammonias (Chart 4(ii)) Nitro compounds (Chart 4(iii)) Nitriles and isonitriles (Chart 4(iv)) Halogen Compounds (Chart 5) Sulfur and Phosphorus Compounds (Chart 6) 86 VU Supplement Quantitative Infrared Analysis Absorbance Slit widths Path lengths Molar absorptivity Attenuated Total Reflectance (ATR) and Multiple Internal Reflectance (MIR) Laser-Raman Spectroscopy The Raman effect Comparison of infrared and Raman spectra 96 Further Reading 98 3 Nuclear Magnetic Resonance Spectroscopy 101 Proton NMR Spectroscopy The NMR Phenomenon The spinning nucleus The effect of an external magnetic field Precessional motion Precessional frequency Energy transitions 106

5 viii CONTENTS 3.2 Theory of Nuclear Magnetic Resonance Chemical Shift and its Measurement Measurement of chemical shift internal standards Measurement of chemical shift the NMR spectrometer Measurement of chemical shift units used in NMR spectroscopy Factors Influencing Chemical Shift Electronegativity shielding and deshielding van der Waals deshielding Anisotropic effects Correlation Data for Proton NMR Spectra Use of correlation tables Influence of restricted rotation Solvents Used in NMR Choice of solvent for proton NMR spectra Solvent shifts concentration and temperature effects hydrogen bonding Integrals in Proton NMR Spectra Spin-Spin Coupling Spin-Spin Splitting The splitting of NMR signals in proton NMR spectra Theory of spin-spin splitting Magnitude of the coupling coupling constants, J More complex spin-spin splitting systems Chemical and magnetic equivalence in NMR Proton-exchange reactions Factors Influencing the Coupling Constant, J General features Factors influencing geminal coupling Factors influencing vicinal coupling Heteronuclear coupling Deuterium exchange Non-first-order Spectra Simplification of Complex Proton NMR Spectra Increased field strength Spin decoupling or double resonance (double irradiation) Lanthanide shift reagents chemical shift reagents Tables of Data for Proton NMR 171

6 CONTENTS Carbon-13 NMR Spectroscopy Natural Abundance 13 C NMR Spectra Resolution Multiplicity : H Decoupling-noise decoupling-broad band decoupling Deuterium coupling NOE signal enhancement Quantitative measurement of line intensities Off-resonance proton decoupling Structural Applications of 13 C NMR Correlation Data for 13 C NMR Spectra Use of the correlation tables Tables of Data for 13 C NMR Spectra 193 ix Supplement Spin-Spin Coupling and Double Irradiation More Advanced Theory Electron-coupled interactions through bonds Energy levels the sign of J Internuclear double resonance (INDOR) and selective population inversion (SPI) Nuclear Overhauser effect (NOE) Variable-temperature NMR The variable-temperature probe Applications Multipulse Techniques in NMR Nett Magnetization Vectors and Rotating Frames CH 3, CH 2 and CH sub-spectra spectrum editing DEPT spectra Gated decoupling and the nuclear Overhauser effect D NMR shift correlation spectra COSY Magnetic Resonance Imaging (MRI) Chemically Induced Dynamic Nuclear Polarization (CIDNP) F and 31 P NMR F NMR P NMR 232

7 X N, 15 N and 17 0 NMR N NMR NMR 235 CONTENTS 35.7 Electron Spin Resonance Spectroscopy (ESR) Derivative curves g values Hyperfine splitting 238 Further Reading Ultraviolet and Visible Spectroscopy Colour and Light Absorption the Chromophore Concept Theory of Electronic Spectroscopy Orbitals involved in electronic transitions Laws of light absorption Beer's and Lambert's laws Conventions Instrumentation and Sampling The ultraviolet-visible spectrometer dispersive, photodiode array and Fourier Transform Instruments Sample and reference cells Solvents and solutions Vacuum ultraviolet Solvent Effects Applications of Electronic Spectroscopy Conjugated Dienes, Trienes and Polyenes Applications of Electronic Spectroscopy Conjugated Poly-ynes and Eneynes Applications of Electronic Spectroscopy afj-unsaturated Carbqnyl Compounds Applications of Electronic Spectroscopy Benzene and its Substitution Derivatives Applications of Electronic Spectroscopy Aromatic Hydrocarbons other than Benzene Applications of Electronic Spectroscopy Heterocyclic Systems Stereochemical Factors in Electronic Spectroscopy Biphenyls and binaphthyls 268

8 CONTENTS cis and trans isomers Angular distortion and cross-conjugation. Steric inhibition of resonance 269 Supplement Quantitative Electronic Spectroscopy Fluorescence and Phosphorescence Absorption Spectra of Charge-transfer Complexes Symmetry Restrictions on the Allowedness of Electronic Transitions Optical Rotatory Dispersion and Circular Dichroism Definitions and nomenclature Cotton effect and stereochemistry The octant rule Electron Spectroscopy for Chemical Analysis (ESCA) 280 Further Reading 282 Xi 5 Mass Spectrometry Basic Principles Instrumentation the Mass Spectrometer Sample insertion inlet systems Ion production in the ionization chamber Separation of the ions in the analyzer The detector-recorder Data handling Isotope Abundances The Molecular Ion Structure of the molecular ion Recognition of the molecular ion Molecular formula from the molecular ion Metastable Ions The nature of metastable ions Ion tube regions Calculation of metastable ion mlz values Significance of metastable ions 303

9 Xii CONTENTS 5.6 Fragmentation Processes Representation of fragmentation processes Basic fragmentation types and rules Factors influencing fragmentations Fragmentations Associated with Functional Groups Alkanes and alkane groups Cycloalkanes Alkenes and alkene groups Cycloalkenes Alkynes Aromatic hydrocarbon groups Halides Alcohols Phenols Ethers, acetals and ketals Carbonyl compounds generally Aldehydes Ketones and quinones Carboxylic acids Esters Amides Anhydrides Acid chlorides Nitriles Nitro compounds Amines and nitrogen heterocycles Sulfur compounds 325 Supplement Alternatives to Electron-impact lonization Chemical ionization Field ionization and field desorption Desorption by lasers, plasmas, ions and atoms LD and LIMA, PD, SIMS and FAB Gas Chromatography-Mass Spectrometry (GC-MS) and High-performance Liquid Chromatography-Mass Spectrometry (HPLC-MS) Isotope Substitution in Mass Spectrometry Isotope Ratios Derivatization of Functional Groups 333

10 CONTENTS 5S.5 Alternatives to Magnetic/Electrostatic Focusing Time-offlight, Quadrupole, Ion Cyclotron, FTICR and Tandem Mass Spectrometers 335 Further Reading 339 Xlll 6 Spectroscopy Problems Infrared Spectroscopy Problems NMR Spectroscopy Problems Electronic Spectroscopy Problems Mass Spectrometry Problems 352 r 6.5 Conjoint IR-UV/VIS-NMR-Mass Spectrometry Problems Solutions to Problems Infrared spectroscopy problems NMR spectroscopy problems Electronic spectroscopy problems Mass spectrometry problems Conjoint spectroscopic problems Answers to Self-assessment Exercises Distributed throughout the Book 375 Appendix 1 Useful Data Correlation Tables and Charts 381 Appendix 2 Acronyms in Spectroscopy 382 Index 384