NMR Spectroscopy Using Liquid Crystal Solvents

Preface

Acknowledgments

Chapter 1. Liquid Crystals

1.1 Introduction

1.2 Classification of Mesophases

1.2.1. The Nematic Mesophase

1.2.2. The Cholesteric Mesophase

1.2.3. Smectic Mesophases

1.3 Effect of Magnetic Fields on Liquid Crystals

1.4 Quantitative Description of Liquid Crystals Ordered by a Magnetic Field

1.5 Nuclear Resonance Spectra of Solutes Dissolved in Liquid Crystals

References

Chapter 2. The Nuclear Spin Hamiltonian for Partially Oriented Molecules

2.1 Introduction

2.2 The Zeeman Term

2.3 Indirect Spin-Spin Coupling

2.4 Dipolar Coupling

2.5 Nuclear Quadrupole Interaction

2.6 Total Anisotropic Spin-Spin Coupling

References

Chapter 3. Analysis of NMR Spectra of Partially Oriented Molecules

3.1 Introduction

3.2 Magnetic Equivalence

3.3 Classification of Spin Systems

3.4 Spin Systems Having Analytical Solutions

3.4.1. An

3.4.2. AB

3.4.3. AB2

3.4.4. AB3

3.4.5. AA'A''A'''

3.4.6. AA'BB'

3.4.7. AA'XX'

3.4.8. AA'A''A'''A''''

3.4.9. A3A3'

3.4.10. AA'A''A'''A''''A'''''

3.5 Analysis of Spin Systems Using the X Approximation

3.6 Computer Analysis

3.7 Multiple Solutions

3.8 Errors on Parameters Determined From Computer Analysis

References

Chapter 4. Determination of the Structure of Rigid Molecules

4.1 Introduction

4.2 Relationship between Dipolar Coupling Constants and Structure

4.3 Vibrational Averaging

4.3.1. Introduction

4.3.2. The Effective Structure

4.4 Example of Rz Structures Determined by NMR

4.4.1. Benzene

4.4.2. Benzene-dl

4.4.3. Pyridine-l5N

4.4.4. Fluorinated Aromatic Compounds

4.4.5. π-Cyclopentadienyl Compounds

4.4.6. Cyclobutadiene Iron Tricarbonyl

4.4.7. Cyclopropane

4.4.8. Cyclopentadiene

4.4.9. π-Allyl Rhenium Tetracarbonyl

4.5 Effect of the Liquid Crystal Phase on the Structure of Solutes

4.5.1. Tetrahedral Molecules

4.5.2. Acetylene

4.5.3. Norbornadiene

4.5.4. Methyl Fluoride

4.5.5. Difluoroethylenes

4.6 Molecular Complexes

4.7 Computational Methods

4.8 Survey of Results

References

Chapter 5. Studies of Internal Motion

5.1 Introduction

5.2 Averaging of Dipolar Couplings

5.2.1. Rotation between Symmetry Related Configurations

5.2.2. Rotation or Exchange between Structures with Symmetry Relationships

5.2.3. Calculation of Rotational Probabilities

5.3. Determination of Barrier Heights

5.3.1. Dependent Internal Rotos

5.4 Comparison Between Structures Determined by NMR and Microwave Spectroscopy for a Molecule with Internal Rotation

5.5 Averaging of Dipolar Couplings Over Ring Puckering Motion

5.6 Valence Isomerisation

5.7 Survey of Results

References

Chapter 6. NMR Spectra From Quadrupolar Nuclei

6.1 Introduction

6.2 Spectra of Nuclei With I=l

6.2.1. A Single Nucleus

6.2.2. A Single Deuterium Coupled to other Nuclei

6.2.3. Two Deuterium Nuclei

6.2.4. Three Nuclei A3 with Symmetry

6.3 Relationship between qzz and Components of q in a Molecule-Fixed Axis System

6.4 Determination of Quadrupole Coupling Constants

6.4.1. Introduction

6.4.2. Examples of Determination of Quadrupole Coupling Constants

6.5 Survey of Results

6.5.1. Deuterium

6.5.2. Nitrogen

6.6 Determination of Orientation From Quadrupole Coupling Constants

6.6.1. Solute Orientation

6.6.2. Orientation of Pure Liquid Crystals

References

Chapter 7. Anisotropy in Nuclear Spin-Spin Coupling

7.1 Introduction

7.2 Theory of Spin-Spin Coupling

7.2.1. The Hamiltonian

7.2.2. Methods of Calculation

7.2.3. Expressions for Jnn, in the Sum Over States Method

7.3 Experimental Determination of Jij aniso

7.3.1. Molecules With Internuclear Vectors Related by a C4 or Higher Axis

7.3.2. Molecules Containing Parallel Internuclear Vectors

7.3.3. Comparison of Observed Dipolar Couplings with those Calculated From a Geometry

7.4 Survey of Experimental Results and Theoretical Calculations

7.4.1. lH-lH Coupling

7.4.2. lH-l3C Coupling

7.4.3. lH-l9F Coupling

7.4.4. lH-X Coupling

7.4.5. l9F-l9F Coupling

7.4.6. l9F-l3C Coupling

7.4.7. l3C-l3C Coupling

7.4.8. l9F-3lP Coupling

References

Chapter 8. Anisotropy in Chemical Shifts

8.1 Introduction

8.2 Theory

8.3 Experimental Methods of Measuring Chemical Shift Anisotropy

8.3.1. Medium Effects on Chemical Shift Anisotropy

8.3.2. Comparison of Chemical Shifts in Nematic and Isotropic Phases

8.3.3. Measurement of Δσ From Dependence of Chemical Shift on Orientation

8.3.4. Measurement of Δσ by Application of an Electric Field

8.3.5. Measurement of Δσ by Sample Rotation

8.3.6. Use of Smectic Phases to Obtain

8.4 Survey of Results

8.4.1. Proton Shielding Anisotropies

8.4.2. Fluorine Shielding Anisotropies

8.4.3. Carbon Shielding Anisotropies

8.4.4. Phosphorus Shielding Anisotropies

8.4.5. Shielding Anisotropies of Other Nuclei

References

Chapter 9. Rotation of Nematic Samples

9.1 Introduction

9.2 Theory

9.3 Separation of Anisotropic From Isotropic Interactions by Sample Rotation

9.3.1. Separation of Jij from Tij

9.3.2. Determination of Chemical Shift Anisotropies by Sample Rotation

References

Chapter 10. Nuclear Magnetic Double Resonance

10.1 Introduction

10.2 Theory

10.3 Spin-Tickling and INDOR

10.3.1. An - {X} With Both Nuclear Spins ½

10.3.2. A3 - {X} System with Both Spins ½

10.3.3. A3 - {X} System with IA = ½, IX = l

10.4 Spin Decoupling

10.4.1. All Nuclei with Spin ½

10.4.2. Systems in Which Irradiated Spins Have S = l

10.4.3. Spin Decoupling With Modulated Irradiating Fields

References

Appendix Recent Publications Not Included in the Text

Index