Chemistry
Understanding NMR
Understanding NMR (nuclear magnetic resonance) involves the study of how atomic nuclei behave in a magnetic field. NMR spectroscopy is a powerful analytical technique used to determine the structure and composition of molecules. By analyzing the interactions between nuclei and magnetic fields, NMR provides valuable information about chemical environments and molecular structures.
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10 Key excerpts on "Understanding NMR"
- SachchidaNand Shukla(Author)
- 2019(Publication Date)
- Arcler Press(Publisher)
Nuclear Magnetic Resonance Spectroscopy (NMR) 5 CONTENTS 5.1. Introduction ................................................................................... 134 5.2. Overview of Concepts ................................................................... 134 5.3. Quantum Mechanical Description ................................................. 137 5.4. Description of The Nuclear Quantum Number ............................... 138 5.5. The Population of The Energy Levels .............................................. 139 5.6. Nmr Spectra of Several Nuclei ....................................................... 142 5.7. Fine Structure of NMR Spectrum .................................................... 147 5.8. Nuclear Relaxation ........................................................................ 151 5.9. The Noe Phenomenon ................................................................... 153 5.10. Use Of Nuclear Magnetic Resonance To Monitor the Rate Processes ....................................................................... 156 5.11. Miscellaneous Uses ..................................................................... 158 References ............................................................................................. 163 Introduction to Modern Instrumentation Methods and Techniques 134 5.1. INTRODUCTION Nuclear magnetic resonance (NMR) spectroscopy was discovered after World War II and from then the applications of NMR spectroscopy to chemistry have been expanding continuously. It was quite natural then that Nuclear magnetic resonance took a vital part in undergraduate chemistry education. In recent years, applications of Nuclear magnetic resonance have been stretched to medicine and biology (Tompa et al., 1996; Bilgic et al., 2015). The fundamental principles are normally covered in physical chemistry course and every undergraduate physical chemistry course textbook includes a chapter on it.
eBook - PDFChemical Analysis
Modern Instrumentation Methods and Techniques
- Francis Rouessac, Annick Rouessac, John Towey(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
NMR spectrometers are therefore often found in research laboratories, although there are routine applications based on this property, using simpler and more robust dedicated instruments (see Figure 15.31). Organic chemists quickly understood the interest of NMR, which has accelerated its development and favoured the appearance of many technical improvements. In this chapter, the method will be illustrated using simple examples chosen specifically for Objectives Describe the basic theory of NMR Interpret an NMR spectrum Measure chemical shifts Study spin coupling Analyse the multiplicity of signals Use a chemical shift table Describe a few applications -CH -CH 2 3 -CH -2 CH -C=O 3 Intensity (arbitary units) NMR 400 MHz CH -C-CH CH 3 2 3 O (TMS) 3.00 2.50 2.00 1.50 1.00 0.50 0.00 ppm Figure 15.1 Conventional representation of the 1 H NMR spectrum of an organic compound. Spectrum of butanone [CH 3 (C=O)CH 2 CH 3 ], with the corresponding integration curve superimposed over the peaks, enabling an evaluation of the relative areas of the main groups of signals identified on the spectrum. The nature of the y -axis scale will be explained later on in the chapter. 389 15.2 Spin/Magnetic Field Interaction for a Nucleus organic chemistry. In short, this method gathers information concerning interactions between the nuclei of certain atoms present in the sample when they are subjected to an intense magnetic field. The basic document, delivered by these instruments, is the NMR spectrum , a graph representing resonance signals whose position, appearance, and intensity constitute a set of information about the sample under examination, which is much easier to interpret if the compound is pure (Figure 15.1). To produce these signals, a second magnetic field, around 10,000 times weaker than the first, is overlaid on the main field and is produced by a source of electromagnetic radiation in the radiofrequency region.
eBook - PDF- David R. Klein(Author)
- 2016(Publication Date)
- Wiley(Publisher)
In this chapter, we will see the role that diamag- netism plays in nuclear magnetic resonance (NMR) spectroscopy, which provides more structural information than any other form of spectroscopy. We will also learn how NMR spectroscopy is used as a pow- erful tool for structure determination. 650 CHAPTER 15 Nuclear Magnetic Resonance Spectroscopy 15.1 Introduction to NMR Spectroscopy Nuclear magnetic resonance (NMR) spectroscopy is arguably the most powerful and broadly appli- cable technique for structure determination available to organic chemists. Indeed, the structure of a compound can often be determined using NMR spectroscopy alone, although in practice, structural determination is generally accomplished through a combination of techniques that includes NMR and IR spectroscopy and mass spectrometry. NMR spectroscopy involves the study of the interaction between electromagnetic radiation and the nuclei of atoms. A wide variety of nuclei can be studied using NMR spectroscopy, including 1 H, 13 C, 15 N, 19 F, and 31 P. In practice, 1 H NMR spectroscopy and 13 C NMR spectroscopy are used most often by organic chemists, because hydrogen and carbon are the primary constituents of organic compounds. Analysis of an NMR spectrum provides information about how the individual carbon and hydrogen atoms are connected to each other in a molecule. This information enables us to determine the carbon- hydrogen framework of a compound, much the way puzzle pieces can be assembled to form a picture. A nucleus with an odd number of protons and/or an odd number of neutrons possesses a quantum mechanical property called nuclear spin, and it can be probed by an NMR spectrometer. Consider the nucleus of a hydrogen atom, which consists of just one proton and therefore has a nuclear spin. Note that this property of spin does not refer to the actual rotation of the proton.
eBook - PDF- Rose Marie O. Mendoza(Author)
- 2019(Publication Date)
- Arcler Press(Publisher)
Nuclear Magnetic Resonance Spectroscopy (NMR) Chapter 5 CONTENTS 5.1. Introduction .................................................................................... 142 5.2. Magnetic Resonance ....................................................................... 143 5.3. Relaxation ...................................................................................... 149 5.4. Other NMR Parameters ................................................................... 157 References ............................................................................................. 161 Elementary Organic Spectroscopy 142 5.1. INTRODUCTION From a purely intellectual point of view, one of the interesting things about NMR (nuclear magnetic resonance) is the intricacy of the subject. However, this intricacy can cause frustration to the people who are willing to understand and utilize NMR. As with the other physical methods used in the studies of the biological systems, NMR may be utilized in the empirical mode; for instance, noting the variations in the NMR parameter with modification of an experimental variable. The better understanding of the NMR phenomenon is usually rewarded with additional clarification of the system under examination. Although there might be thresholds of the knowledge of NMR essential to read the text critically or to perform the NMR studies, there is variety of the knowledge to be achieved about the NMR which has the practical surplus of providing the greater variety of NMR experiments to be correctly utilized (Bloembergen et al., 1948) (Figure 5.1). Figure 5.1: Schematic representation of NMR. Source: https://chembam.com/techniques/nmr/ The NMR phenomenon can usually be described in the nutshell as follows. If the sample is placed in the magnetic field (MF) and is given RF radiation at a suitable frequency, nuclei in the sample are able to absorb the energy.
eBook - PDF- Satinder Ahuja, Neil Jespersen(Authors)
- 2006(Publication Date)
- Elsevier Science(Publisher)
Chapter 10 Nuclear magnetic resonance spectroscopy Linda Lohr, Brian Marquez and Gary Martin 10.1 INTRODUCTION Nuclear magnetic resonance (NMR) is amenable to a broad range of applications. It has found wide utility in the pharmaceutical, medical and petrochemical industries as well as across the polymer, materials science, cellulose, pigment, and catalysis fields to name just as a few examples. The vast diversity of NMR applications may be in part due to its profound ability to probe both chemical and physical properties in-cluding chemical structure as well as molecular dynamics. This gives NMR the potential to have a great breadth of impact compared with other analytical techniques. Furthermore, it can be applied to liquids, solids or gases. In some ways, it is a ‘‘universal detector’’ in that it detects all irradiated nuclei in a sample regardless of the source. Signals appear from all components in a mixture, proportional to their concentration. NMR is therefore a natural compliment to separation techniques such as chromatography, which provide a high degree of component selectivity in a mixture. NMR is also a logical compliment to mass spectrometry, since it can provide critical structural information. Compared to other solid-state techniques, NMR is exquisitely sensitive to small changes in local electronic environments, such as discerning individual polymorphs in a crystalline mixture. Beyond the qualitative molecular information afforded by NMR, one can also obtain quantitative information. Depending on the sample, NMR can measure relative quantities of components in a mixture as low as 0.1–1% in the solid state. NMR limits of detection are much lower in the liquid state, often as low as 1000:1 down to 10,000:1. In-ternal standards can be used to translate these values into absolute quantities. Of course, the limit of quantitation is not only dependent on Comprehensive Analytical Chemistry 47 S.
eBook - PDF- David R. Klein(Author)
- 2020(Publication Date)
- Wiley(Publisher)
In this chapter, we will see the role that diamagnetism plays in nuclear magnetic reso- nance (NMR) spectroscopy, which provides more structural information than any other form of spectroscopy. We will also learn how NMR spectroscopy is used as a power- ful tool for structure determination. 696 CHAPTER 16 Nuclear Magnetic Resonance Spectroscopy 16.1 INTRODUCTION TO NMR SPECTROSCOPY Nuclear magnetic resonance (NMR) spectroscopy is arguably the most powerful and broadly appli- cable technique for structure determination available to organic chemists. Indeed, the structure of a compound can often be determined using NMR spectroscopy alone, although in practice, structural determination is generally accomplished through a combination of techniques that includes NMR and IR spectroscopy and mass spectrometry. NMR spectroscopy involves the study of the interaction between electromagnetic radiation and the nuclei of atoms. A wide variety of nuclei can be studied using NMR spectroscopy, including 1 H, 13 C, 15 N, 19 F, and 31 P. In practice, 1 H NMR spectroscopy and 13 C NMR spectroscopy are used most often by organic chemists, because hydrogen and carbon are the primary constituents of organic compounds. Analysis of an NMR spectrum provides information about how the individual carbon and hydrogen atoms are connected to each other in a molecule. This information enables us to determine the carbon- hydrogen framework of a compound, much the way puzzle pieces can be assembled to form a picture. A nucleus with an odd number of protons and/or an odd number of neutrons possesses a quantum mechanical property called nuclear spin, and it can be probed by an NMR spectrometer. Consider the nucleus of a hydrogen atom, which consists of just one proton and therefore has a nuclear spin. Note that this property of spin does not refer to the actual rotation of the proton.
- Kenneth Williamson, Katherine Masters(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
These small varia-tions, called chemical shifts, are plotted versus signal intensity to produce the NMR spectrum. The interpretation of these signals and other spectral features such as splitting patterns and peak areas, as described in the following sections, facilitates organic structure elucidation. 1 H NMR: Determination of the number, kind, and relative locations of hydrogen atoms (protons) in a molecule. Chemical shift, δ (ppm) Nuclear Magnetic Resonance Spectroscopy CHAPTER 12 PRE-LAB EXERCISE: Outline the preliminary solubility experiments you would carry out using inexpensive solvents before preparing a solution of an unknown compound for nuclear magnetic resonance (NMR) spectros-copy using expensive deuterated solvents. 240 Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 241 Chapter 12 ■ Nuclear Magnetic Resonance Spectroscopy I N T E R P R E T A T I O N O F 1 H N M R S P E C T R A There are two approaches to interpreting proton NMR spectra as follows: 1. The structure from the spectrum approach is the strategy of using the informa-tion in the NMR spectrum to draw the structure of the molecule based on ref-erence tables and rules. This approach is used if the compound’s structure is unknown. In this case, the NMR spectrum alone is often insufficient to “solve” the complete structure and must be combined with knowledge about the com-pound’s source (synthetic reaction or natural product) and complementary spectral data (infrared, ultraviolet, and/or mass spectrometric).
eBook - PDF- David R. Klein(Author)
- 2021(Publication Date)
- Wiley(Publisher)
NMR spectroscopy involves the study of the interaction between electromagnetic radiation and the nuclei of atoms. A wide variety of nuclei can be studied using NMR spectroscopy, including 1 H, 13 C, 15 N, 19 F, and 31 P. In practice, 1 H NMR spectroscopy and 13 C NMR spectroscopy are used most often by organic chemists, because hydrogen and carbon are the primary constituents of organic compounds. Analysis of an NMR spectrum provides information about how the individual carbon and hydrogen atoms are connected to each other in a molecule. This information enables us to determine the carbon- hydrogen framework of a compound, much the way puzzle pieces can be assembled to form a picture. A nucleus with an odd number of protons and/or an odd number of neutrons possesses a quan- tum mechanical property called nuclear spin, and it can be probed by an NMR spectrometer. Con- sider the nucleus of a hydrogen atom, which consists of just one proton and therefore has a nuclear spin. Note that this property of spin does not refer to the actual rotation of the proton. Nevertheless, it is a useful analogy to consider. A spinning proton can be viewed as a rotating sphere of charge, which generates a magnetic field, called a magnetic moment. The magnetic moment of a spinning proton is similar to the magnetic field produced by a bar magnet (Figure 15.1). FIGURE 15.1 (a) The magnetic moment of a spinning proton. (b) The magnetic field of a bar magnet. Direction of rotation N S Axis of spin and of the magnetic moment Magnetic lines of force N S (a) (b) DO YOU REMEMBER? Before you go on, be sure you understand the following topics.
eBook - PDF- J.R.J. Paré, J.M.R. Bélanger(Authors)
- 1997(Publication Date)
- Elsevier Science(Publisher)
J.R.J. Par~ and J.M.R. B~langer (Editors) Instrumental Methods in Food Analysis 9 1997 Elsevier Science B.V. All rights reserved. Chapter 6 Nuclear Magnetic Resonance Spectroscopy (NMR): Principles and Applications Calin Deleanu (1) and J. R. Jocelyn Par~ (2) 1) Costin D. Nenitescu Institute of Organic Chemistry, NMR Department, Spl. Independentei 202 B, P. O. Box 15-258, Bucharest, Romania and 2) Environment Canada, Environmental Technology Centre Ottawa, ON, Canada KIA 0H3 6.1 INTRODUCTION The Nuclear Magnetic Resonance (NMR) technique is now half a century old [1,2]. One might consider this as a long time, or at least as a time sufficiently long to justify the fact that NMR is by now a technique present in both advanced research and basic undergraduate courses in so many fields like chemistry, physics, biology, food sciences, medicine, material sciences, and so on. But if we consider the formidable progress that took place in these years, with NMR opening several stand-alone research fields (to mention only liquid-, solid-, localized-, low resolution-NMR, NMR Imaging and Microscopy) and the explosion of new techniques and instrumentation, then 50 years is a rather short time. By now, high resolution NMR is the most powerful technique for structure elucidation of chemical compounds in solution. It is also one of the most expensive techniques in terms of equipment, but meanwhile, very significantly, a technique which is already part of almost all research and teaching establishments. While the manufacturers are continuously pushing the limits of the instrumentation, trying to cope with every day developments in theoretical knowledge, the research, teaching and health establishments keep buying equipment costing roughly a million US
eBook - PDFNuclear Magnetic Resonance
Volume 36
- G A Webb(Author)
- 2007(Publication Date)
- Royal Society of Chemistry(Publisher)
Of course, such a distinction is sometimes problematic, as innovative work dealing with solutions of complex molecules may be of interest for research in the field covered here. Thus, at the risk of duplication, some interesting studies dealing with more complex systems are mentioned briefly. The subsection ‘‘Molten Salts’’ is replaced by the subsection ‘‘Ionic Liquids and Molten Salts’’ taking into account the increasing importance of this new class of materials. At the beginning of this chapter it is convenient to quote some authoritative reviews in the subject area. More specialized reviews will be discussed in the corresponding subsections. Details will be discussed later in this chapter. The year 2006 represents the 60th anniversary of nuclear magnetic resonance (NMR) spectro-scopy. It is therefore appropriate and indeed valuable to reflect on how this versatile methodology has developed, expanded, and evolved into a cornerstone of chemical research since 1946. Darbeau 2 provided an overview of NMR spectroscopy includ-ing the basic principles of NMR the historical development of the field and a few unique applications of the methodology. Bagno et al . 3 reviewed NMR techniques for the investigation of solvation phenomena and non-covalent interactions. Solvent effects; non-covalent inter-actions, spin–spin couplings; intermolecular NOE; spin–lattice relaxation and diffu-sion coefficients are discussed. Yonker and Linehan 4 reported the use of supercritical fluids as solvents for NMR spectroscopy. The topics of high-pressure NMR; catalysis; phase equilibrium; molecular dynamics; diffusion coefficients and hydro-gen bonding were considered. Brand et al . 5 discussed intermolecular interaction as investigated by NOE and diffusion studies. Fantazzini and Brown 6 reported the fact that distributions of relaxation times or rates may be misinterpreted or wrongly compared if units are not consistently used or not correctly identified.
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